1598709600

Given two binary arrays **A[]** and **B[]**, of length **N** and **M** respectively, the task is to find the number of rectangles of area **K** consisting of **1**‘s in the matrix **C[][]** generated by multiplying the two arrays such that, **C[i][j] = A[i] * B[j] **( 1 __<__ i __<__ n, 1 __<__ j __<__ m).

**Examples:**

_ N= 3, M = 3, A[] = {1, 1, 0}, B[] = {0, 1, 1}, K = 2_Input:

_ 4_Output:

_ C[][] = {{0, 1, 1}, {0, 1, 1}, {0, 0, 0}}_Explanation:

```
0 1 1 0 1 1 0 1 1 0 1 1
0 1 1 0 1 1 0 1 1 0 1 1
0 0 0 0 0 0 0 0 0 0 0 0
```

Therefore, there are 4 possible rectangles of area 2 from the matrix.

_ N = 4, M = 2, A[] = {0, 0, 1, 1}, B[] = {1, 0, 1}, K = 2_Input:

_ 2_Output:

_ C[][] = {{0, 0, 0}, {0, 0, 0}, {1, 0, 1}, {1, 0, 1}}_Explanation:

```
0 0 0 0 0 0
0 0 0 0 0 0
1 0 1 1 0 1
1 0 1 1 0 1
```

Therefore, there are 2 possible rectangles of area 2 in the matrix.

**Naive Approach: **The simplest approach to solve the problem is to **generate the required matrix** by multiplying the two arrays and for every possible rectangle of area **K, **check if it consists of only 1’s or not…

** Time Complexity:**_ O(N * M * K)_

** Auxiliary Space:**_ O(N * M)_

**Efficient Approach: **To optimize the above approach, the following observations need to be made instead of generating the matrix:

- _The __area of a rectangle is equal to the product of its _
**_length _**_and _*breadth.* - _Using this property, visualize the rectangle as a
which contains only _*submatrix**1**s. Therefore, this submatrix is the result of the product of two subarrays of length a, b where*.*a * b = K* *Since the submatrix contains only*‘s, it is obvious that these two subarrays also contain only*1*‘s in them.*1*

Therefore, the problem reduces to finding the subarrays consisting of only **1**‘s of all possible lengths which are proper divisors of **K**, from the arrays **A[]** and **B[]**. Follow the steps below to solve the problem:

- Precalculate the count of possible subarrays.
- Iterate through all the divisors of
**K**and for each possible pair (**p, q**) where**p * q = K**, check if there exist subarrays of length p, q in A[] and B[]. - Increase the count of possible such subarrays accordingly and finally, print the obtained count.

Below is the implementation of the above approach:

- C++

`// C++ Program to implement`

`// the above approach`

`#include <bits/stdc++.h>`

`**using**`

`**namespace**`

`std;`

`// Function to find the subarrays of`

`// all possible lengths made up of only 1s`

`vector<``**int**``> findSubarrays(vector<``**int**``>& a)`

`{`

`**int**`

`n = a.size();`

`// Stores the frequency`

`// of the subarrays`

`vector<``**int**``> freq(n + 1);`

`**int**`

`count = 0;`

`**for**`

`(``**int**`

`i = 0; i < n; i++) {`

`**if**`

`(a[i] == 0) {`

`// Check if the previous`

`// value was also 0`

`**if**`

`(count == 0)`

`**continue**``;`

`// If the previous value was 1`

`**else**`

`{`

`**int**`

`value = count;`

`**for**`

`(``**int**`

`j = 1; j <= count; j++) {`

`// Find the subarrays of`

`// each size from 1 to count`

`freq[j] += value;`

`value--;`

`}`

`count = 0;`

`}`

`}`

`**else**`

`count++;`

`}`

`// If A[] is of the form ....111`

`**if**`

`(count > 0) {`

`**int**`

`value = count;`

`**for**`

`(``**int**`

`j = 1; j <= count; j++) {`

`freq[j] += value;`

`value--;`

`}`

`}`

`**return**`

`freq;`

`}`

`// Function to find the count`

`// of all possible rectangles`

`**void**`

`countRectangles(vector<``**int**``>& a,`

`vector<``**int**``>& b,`

`**int**`

`K)`

`{`

`// Size of each of the arrays`

`**int**`

`n = a.size();`

`**int**`

`m = b.size();`

`// Stores the count of subarrays`

`// of each size consisting of`

`// only 1s from array A[]`

`vector<``**int**``> subA`

`= findSubarrays(a);`

`// Stores the count of subarrays`

`// of each size consisting of`

`// only 1s from array B[]`

`vector<``**int**``> subB`

`= findSubarrays(b);`

`**int**`

`total = 0;`

`// Iterating over all subarrays`

`// consisting of only 1s in A[]`

`**for**`

`(``**int**`

`i = 1; i < subA.size(); i++) {`

`// If i is a factor of K, then`

`// there is a subarray of size K/i in B[]`

`**if**`

`(K % i == 0 and (K / i) <= m) {`

`total = total + subA[i] * subB[K / i];`

`}`

`}`

`cout << total;`

`}`

`// Driver Code`

`**int**`

`main()`

`{`

`vector<``**int**``> a = { 0, 0, 1, 1 };`

`vector<``**int**``> b = { 1, 0, 1 };`

`**int**`

`K = 2;`

`countRectangles(a, b, K);`

`**return**`

`0;`

`}`

**Output:**

```
2
```

** Time Complexity:**_ O(D) * O(N + M), where D is the number of divisors of K._

** Auxiliary Space:**_ O(N + M)_

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the **DSA Self Paced Course** at a student-friendly price and become industry ready.

#arrays #geometric #mathematical #matrix #searching #area-volume-programs #binary-representation #square-rectangle #subarray #submatrix

1666082925

This tutorialvideo on 'Arrays in Python' will help you establish a strong hold on all the fundamentals in python programming language. Below are the topics covered in this video:

1:15 What is an array?

2:53 Is python list same as an array?

3:48 How to create arrays in python?

7:19 Accessing array elements

9:59 Basic array operations

- 10:33 Finding the length of an array

- 11:44 Adding Elements

- 15:06 Removing elements

- 18:32 Array concatenation

- 20:59 Slicing

- 23:26 Looping

**Python Array Tutorial – Define, Index, Methods**

In this article, you'll learn how to use Python arrays. You'll see how to define them and the different methods commonly used for performing operations on them.

The artcile covers arrays that you create by importing the `array module`

. We won't cover NumPy arrays here.

- Introduction to Arrays
- The differences between Lists and Arrays
- When to use arrays

- How to use arrays
- Define arrays
- Find the length of arrays
- Array indexing
- Search through arrays
- Loop through arrays
- Slice an array

- Array methods for performing operations
- Change an existing value
- Add a new value
- Remove a value

- Conclusion

Let's get started!

Arrays are a fundamental data structure, and an important part of most programming languages. In Python, they are containers which are able to store more than one item at the same time.

Specifically, they are an ordered collection of elements with every value being of the same data type. That is the most important thing to remember about Python arrays - the fact that they can only hold a sequence of multiple items that are of the same type.

Lists are one of the most common data structures in Python, and a core part of the language.

Lists and arrays behave similarly.

Just like arrays, lists are an ordered sequence of elements.

They are also mutable and not fixed in size, which means they can grow and shrink throughout the life of the program. Items can be added and removed, making them very flexible to work with.

However, lists and arrays are **not** the same thing.

**Lists** store items that are of **various data types**. This means that a list can contain integers, floating point numbers, strings, or any other Python data type, at the same time. That is not the case with arrays.

As mentioned in the section above, **arrays** store only items that are of the **same single data type**. There are arrays that contain only integers, or only floating point numbers, or only any other Python data type you want to use.

Lists are built into the Python programming language, whereas arrays aren't. Arrays are not a built-in data structure, and therefore need to be imported via the `array module`

in order to be used.

Arrays of the `array module`

are a thin wrapper over C arrays, and are useful when you want to work with homogeneous data.

They are also more compact and take up less memory and space which makes them more size efficient compared to lists.

If you want to perform mathematical calculations, then you should use NumPy arrays by importing the NumPy package. Besides that, you should just use Python arrays when you really need to, as lists work in a similar way and are more flexible to work with.

In order to create Python arrays, you'll first have to import the `array module`

which contains all the necassary functions.

There are three ways you can import the `array module`

:

- By using
`import array`

at the top of the file. This includes the module`array`

. You would then go on to create an array using`array.array()`

.

```
import array
#how you would create an array
array.array()
```

- Instead of having to type
`array.array()`

all the time, you could use`import array as arr`

at the top of the file, instead of`import array`

alone. You would then create an array by typing`arr.array()`

. The`arr`

acts as an alias name, with the array constructor then immediately following it.

```
import array as arr
#how you would create an array
arr.array()
```

- Lastly, you could also use
`from array import *`

, with`*`

importing all the functionalities available. You would then create an array by writing the`array()`

constructor alone.

```
from array import *
#how you would create an array
array()
```

Once you've imported the `array module`

, you can then go on to define a Python array.

The general syntax for creating an array looks like this:

`variable_name = array(typecode,[elements])`

Let's break it down:

`variable_name`

would be the name of the array.- The
`typecode`

specifies what kind of elements would be stored in the array. Whether it would be an array of integers, an array of floats or an array of any other Python data type. Remember that all elements should be of the same data type. - Inside square brackets you mention the
`elements`

that would be stored in the array, with each element being separated by a comma. You can also create an*empty*array by just writing`variable_name = array(typecode)`

alone, without any elements.

Below is a typecode table, with the different typecodes that can be used with the different data types when defining Python arrays:

TYPECODE | C TYPE | PYTHON TYPE | SIZE |
---|---|---|---|

'b' | signed char | int | 1 |

'B' | unsigned char | int | 1 |

'u' | wchar_t | Unicode character | 2 |

'h' | signed short | int | 2 |

'H' | unsigned short | int | 2 |

'i' | signed int | int | 2 |

'I' | unsigned int | int | 2 |

'l' | signed long | int | 4 |

'L' | unsigned long | int | 4 |

'q' | signed long long | int | 8 |

'Q' | unsigned long long | int | 8 |

'f' | float | float | 4 |

'd' | double | float | 8 |

Tying everything together, here is an example of how you would define an array in Python:

```
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers)
#output
#array('i', [10, 20, 30])
```

Let's break it down:

- First we included the array module, in this case with
`import array as arr`

. - Then, we created a
`numbers`

array. - We used
`arr.array()`

because of`import array as arr`

. - Inside the
`array()`

constructor, we first included`i`

, for signed integer. Signed integer means that the array can include positive*and*negative values. Unsigned integer, with`H`

for example, would mean that no negative values are allowed. - Lastly, we included the values to be stored in the array in square brackets.

Keep in mind that if you tried to include values that were not of `i`

typecode, meaning they were not integer values, you would get an error:

```
import array as arr
numbers = arr.array('i',[10.0,20,30])
print(numbers)
#output
#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 14, in <module>
# numbers = arr.array('i',[10.0,20,30])
#TypeError: 'float' object cannot be interpreted as an integer
```

In the example above, I tried to include a floating point number in the array. I got an error because this is meant to be an integer array only.

Another way to create an array is the following:

```
from array import *
#an array of floating point values
numbers = array('d',[10.0,20.0,30.0])
print(numbers)
#output
#array('d', [10.0, 20.0, 30.0])
```

The example above imported the `array module`

via `from array import *`

and created an array `numbers`

of float data type. This means that it holds only floating point numbers, which is specified with the `'d'`

typecode.

To find out the exact number of elements contained in an array, use the built-in `len()`

method.

It will return the integer number that is equal to the total number of elements in the array you specify.

```
import array as arr
numbers = arr.array('i',[10,20,30])
print(len(numbers))
#output
# 3
```

In the example above, the array contained three elements – `10, 20, 30`

– so the length of `numbers`

is `3`

.

Each item in an array has a specific address. Individual items are accessed by referencing their *index number*.

Indexing in Python, and in all programming languages and computing in general, starts at `0`

. It is important to remember that counting starts at `0`

and **not** at `1`

.

To access an element, you first write the name of the array followed by square brackets. Inside the square brackets you include the item's index number.

The general syntax would look something like this:

`array_name[index_value_of_item]`

Here is how you would access each individual element in an array:

```
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers[0]) # gets the 1st element
print(numbers[1]) # gets the 2nd element
print(numbers[2]) # gets the 3rd element
#output
#10
#20
#30
```

Remember that the index value of the last element of an array is always one less than the length of the array. Where `n`

is the length of the array, `n - 1`

will be the index value of the last item.

Note that you can also access each individual element using negative indexing.

With negative indexing, the last element would have an index of `-1`

, the second to last element would have an index of `-2`

, and so on.

Here is how you would get each item in an array using that method:

```
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers[-1]) #gets last item
print(numbers[-2]) #gets second to last item
print(numbers[-3]) #gets first item
#output
#30
#20
#10
```

You can find out an element's index number by using the `index()`

method.

You pass the value of the element being searched as the argument to the method, and the element's index number is returned.

```
import array as arr
numbers = arr.array('i',[10,20,30])
#search for the index of the value 10
print(numbers.index(10))
#output
#0
```

If there is more than one element with the same value, the index of the first instance of the value will be returned:

```
import array as arr
numbers = arr.array('i',[10,20,30,10,20,30])
#search for the index of the value 10
#will return the index number of the first instance of the value 10
print(numbers.index(10))
#output
#0
```

You've seen how to access each individual element in an array and print it out on its own.

You've also seen how to print the array, using the `print()`

method. That method gives the following result:

```
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers)
#output
#array('i', [10, 20, 30])
```

What if you want to print each value one by one?

This is where a loop comes in handy. You can loop through the array and print out each value, one-by-one, with each loop iteration.

For this you can use a simple `for`

loop:

```
import array as arr
numbers = arr.array('i',[10,20,30])
for number in numbers:
print(number)
#output
#10
#20
#30
```

You could also use the `range()`

function, and pass the `len()`

method as its parameter. This would give the same result as above:

```
import array as arr
values = arr.array('i',[10,20,30])
#prints each individual value in the array
for value in range(len(values)):
print(values[value])
#output
#10
#20
#30
```

To access a specific range of values inside the array, use the slicing operator, which is a colon `:`

.

When using the slicing operator and you only include one value, the counting starts from `0`

by default. It gets the first item, and goes up to but not including the index number you specify.

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#get the values 10 and 20 only
print(numbers[:2]) #first to second position
#output
#array('i', [10, 20])
```

When you pass two numbers as arguments, you specify a range of numbers. In this case, the counting starts at the position of the first number in the range, and up to but not including the second one:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#get the values 20 and 30 only
print(numbers[1:3]) #second to third position
#output
#rray('i', [20, 30])
```

Arrays are mutable, which means they are changeable. You can change the value of the different items, add new ones, or remove any you don't want in your program anymore.

Let's see some of the most commonly used methods which are used for performing operations on arrays.

You can change the value of a specific element by speficying its position and assigning it a new value:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#change the first element
#change it from having a value of 10 to having a value of 40
numbers[0] = 40
print(numbers)
#output
#array('i', [40, 20, 30])
```

To add one single value at the end of an array, use the `append()`

method:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 to the end of numbers
numbers.append(40)
print(numbers)
#output
#array('i', [10, 20, 30, 40])
```

Be aware that the new item you add needs to be the same data type as the rest of the items in the array.

Look what happens when I try to add a float to an array of integers:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 to the end of numbers
numbers.append(40.0)
print(numbers)
#output
#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 19, in <module>
# numbers.append(40.0)
#TypeError: 'float' object cannot be interpreted as an integer
```

But what if you want to add more than one value to the end an array?

Use the `extend()`

method, which takes an iterable (such as a list of items) as an argument. Again, make sure that the new items are all the same data type.

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integers 40,50,60 to the end of numbers
#The numbers need to be enclosed in square brackets
numbers.extend([40,50,60])
print(numbers)
#output
#array('i', [10, 20, 30, 40, 50, 60])
```

And what if you don't want to add an item to the end of an array? Use the `insert()`

method, to add an item at a specific position.

The `insert()`

function takes two arguments: the index number of the position the new element will be inserted, and the value of the new element.

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 in the first position
#remember indexing starts at 0
numbers.insert(0,40)
print(numbers)
#output
#array('i', [40, 10, 20, 30])
```

To remove an element from an array, use the `remove()`

method and include the value as an argument to the method.

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
numbers.remove(10)
print(numbers)
#output
#array('i', [20, 30])
```

With `remove()`

, only the first instance of the value you pass as an argument will be removed.

See what happens when there are more than one identical values:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30,10,20])
numbers.remove(10)
print(numbers)
#output
#array('i', [20, 30, 10, 20])
```

Only the first occurence of `10`

is removed.

You can also use the `pop()`

method, and specify the position of the element to be removed:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30,10,20])
#remove the first instance of 10
numbers.pop(0)
print(numbers)
#output
#array('i', [20, 30, 10, 20])
```

And there you have it - you now know the basics of how to create arrays in Python using the `array module`

. Hopefully you found this guide helpful.

Thanks for reading and happy coding!

#python #programming

1670560264

## Learn how to use Python arrays. Create arrays in Python using the array module. You'll see how to define them and the different methods commonly used for performing operations on them.

The artcile covers arrays that you create by importing the `array module`

. We won't cover NumPy arrays here.

- Introduction to Arrays
- The differences between Lists and Arrays
- When to use arrays

- How to use arrays
- Define arrays
- Find the length of arrays
- Array indexing
- Search through arrays
- Loop through arrays
- Slice an array

- Array methods for performing operations
- Change an existing value
- Add a new value
- Remove a value

- Conclusion

Let's get started!

Arrays are a fundamental data structure, and an important part of most programming languages. In Python, they are containers which are able to store more than one item at the same time.

Specifically, they are an ordered collection of elements with every value being of the same data type. That is the most important thing to remember about Python arrays - the fact that they can only hold a sequence of multiple items that are of the same type.

Lists are one of the most common data structures in Python, and a core part of the language.

Lists and arrays behave similarly.

Just like arrays, lists are an ordered sequence of elements.

They are also mutable and not fixed in size, which means they can grow and shrink throughout the life of the program. Items can be added and removed, making them very flexible to work with.

However, lists and arrays are **not** the same thing.

**Lists** store items that are of **various data types**. This means that a list can contain integers, floating point numbers, strings, or any other Python data type, at the same time. That is not the case with arrays.

As mentioned in the section above, **arrays** store only items that are of the **same single data type**. There are arrays that contain only integers, or only floating point numbers, or only any other Python data type you want to use.

Lists are built into the Python programming language, whereas arrays aren't. Arrays are not a built-in data structure, and therefore need to be imported via the `array module`

in order to be used.

Arrays of the `array module`

are a thin wrapper over C arrays, and are useful when you want to work with homogeneous data.

They are also more compact and take up less memory and space which makes them more size efficient compared to lists.

If you want to perform mathematical calculations, then you should use NumPy arrays by importing the NumPy package. Besides that, you should just use Python arrays when you really need to, as lists work in a similar way and are more flexible to work with.

In order to create Python arrays, you'll first have to import the `array module`

which contains all the necassary functions.

There are three ways you can import the `array module`

:

- By using
`import array`

at the top of the file. This includes the module`array`

. You would then go on to create an array using`array.array()`

.

```
import array
#how you would create an array
array.array()
```

- Instead of having to type
`array.array()`

all the time, you could use`import array as arr`

at the top of the file, instead of`import array`

alone. You would then create an array by typing`arr.array()`

. The`arr`

acts as an alias name, with the array constructor then immediately following it.

```
import array as arr
#how you would create an array
arr.array()
```

- Lastly, you could also use
`from array import *`

, with`*`

importing all the functionalities available. You would then create an array by writing the`array()`

constructor alone.

```
from array import *
#how you would create an array
array()
```

Once you've imported the `array module`

, you can then go on to define a Python array.

The general syntax for creating an array looks like this:

```
variable_name = array(typecode,[elements])
```

Let's break it down:

`variable_name`

would be the name of the array.- The
`typecode`

specifies what kind of elements would be stored in the array. Whether it would be an array of integers, an array of floats or an array of any other Python data type. Remember that all elements should be of the same data type. - Inside square brackets you mention the
`elements`

that would be stored in the array, with each element being separated by a comma. You can also create an*empty*array by just writing`variable_name = array(typecode)`

alone, without any elements.

Below is a typecode table, with the different typecodes that can be used with the different data types when defining Python arrays:

TYPECODE | C TYPE | PYTHON TYPE | SIZE |
---|---|---|---|

'b' | signed char | int | 1 |

'B' | unsigned char | int | 1 |

'u' | wchar_t | Unicode character | 2 |

'h' | signed short | int | 2 |

'H' | unsigned short | int | 2 |

'i' | signed int | int | 2 |

'I' | unsigned int | int | 2 |

'l' | signed long | int | 4 |

'L' | unsigned long | int | 4 |

'q' | signed long long | int | 8 |

'Q' | unsigned long long | int | 8 |

'f' | float | float | 4 |

'd' | double | float | 8 |

Tying everything together, here is an example of how you would define an array in Python:

```
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers)
#output
#array('i', [10, 20, 30])
```

Let's break it down:

- First we included the array module, in this case with
`import array as arr`

. - Then, we created a
`numbers`

array. - We used
`arr.array()`

because of`import array as arr`

. - Inside the
`array()`

constructor, we first included`i`

, for signed integer. Signed integer means that the array can include positive*and*negative values. Unsigned integer, with`H`

for example, would mean that no negative values are allowed. - Lastly, we included the values to be stored in the array in square brackets.

Keep in mind that if you tried to include values that were not of `i`

typecode, meaning they were not integer values, you would get an error:

```
import array as arr
numbers = arr.array('i',[10.0,20,30])
print(numbers)
#output
#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 14, in <module>
# numbers = arr.array('i',[10.0,20,30])
#TypeError: 'float' object cannot be interpreted as an integer
```

In the example above, I tried to include a floating point number in the array. I got an error because this is meant to be an integer array only.

Another way to create an array is the following:

```
from array import *
#an array of floating point values
numbers = array('d',[10.0,20.0,30.0])
print(numbers)
#output
#array('d', [10.0, 20.0, 30.0])
```

The example above imported the `array module`

via `from array import *`

and created an array `numbers`

of float data type. This means that it holds only floating point numbers, which is specified with the `'d'`

typecode.

To find out the exact number of elements contained in an array, use the built-in `len()`

method.

It will return the integer number that is equal to the total number of elements in the array you specify.

```
import array as arr
numbers = arr.array('i',[10,20,30])
print(len(numbers))
#output
# 3
```

In the example above, the array contained three elements – `10, 20, 30`

– so the length of `numbers`

is `3`

.

Each item in an array has a specific address. Individual items are accessed by referencing their *index number*.

Indexing in Python, and in all programming languages and computing in general, starts at `0`

. It is important to remember that counting starts at `0`

and **not** at `1`

.

To access an element, you first write the name of the array followed by square brackets. Inside the square brackets you include the item's index number.

The general syntax would look something like this:

```
array_name[index_value_of_item]
```

Here is how you would access each individual element in an array:

```
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers[0]) # gets the 1st element
print(numbers[1]) # gets the 2nd element
print(numbers[2]) # gets the 3rd element
#output
#10
#20
#30
```

Remember that the index value of the last element of an array is always one less than the length of the array. Where `n`

is the length of the array, `n - 1`

will be the index value of the last item.

Note that you can also access each individual element using negative indexing.

With negative indexing, the last element would have an index of `-1`

, the second to last element would have an index of `-2`

, and so on.

Here is how you would get each item in an array using that method:

```
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers[-1]) #gets last item
print(numbers[-2]) #gets second to last item
print(numbers[-3]) #gets first item
#output
#30
#20
#10
```

You can find out an element's index number by using the `index()`

method.

You pass the value of the element being searched as the argument to the method, and the element's index number is returned.

```
import array as arr
numbers = arr.array('i',[10,20,30])
#search for the index of the value 10
print(numbers.index(10))
#output
#0
```

If there is more than one element with the same value, the index of the first instance of the value will be returned:

```
import array as arr
numbers = arr.array('i',[10,20,30,10,20,30])
#search for the index of the value 10
#will return the index number of the first instance of the value 10
print(numbers.index(10))
#output
#0
```

You've seen how to access each individual element in an array and print it out on its own.

You've also seen how to print the array, using the `print()`

method. That method gives the following result:

```
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers)
#output
#array('i', [10, 20, 30])
```

What if you want to print each value one by one?

This is where a loop comes in handy. You can loop through the array and print out each value, one-by-one, with each loop iteration.

For this you can use a simple `for`

loop:

```
import array as arr
numbers = arr.array('i',[10,20,30])
for number in numbers:
print(number)
#output
#10
#20
#30
```

You could also use the `range()`

function, and pass the `len()`

method as its parameter. This would give the same result as above:

```
import array as arr
values = arr.array('i',[10,20,30])
#prints each individual value in the array
for value in range(len(values)):
print(values[value])
#output
#10
#20
#30
```

To access a specific range of values inside the array, use the slicing operator, which is a colon `:`

.

When using the slicing operator and you only include one value, the counting starts from `0`

by default. It gets the first item, and goes up to but not including the index number you specify.

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#get the values 10 and 20 only
print(numbers[:2]) #first to second position
#output
#array('i', [10, 20])
```

When you pass two numbers as arguments, you specify a range of numbers. In this case, the counting starts at the position of the first number in the range, and up to but not including the second one:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#get the values 20 and 30 only
print(numbers[1:3]) #second to third position
#output
#rray('i', [20, 30])
```

Arrays are mutable, which means they are changeable. You can change the value of the different items, add new ones, or remove any you don't want in your program anymore.

Let's see some of the most commonly used methods which are used for performing operations on arrays.

You can change the value of a specific element by speficying its position and assigning it a new value:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#change the first element
#change it from having a value of 10 to having a value of 40
numbers[0] = 40
print(numbers)
#output
#array('i', [40, 20, 30])
```

To add one single value at the end of an array, use the `append()`

method:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 to the end of numbers
numbers.append(40)
print(numbers)
#output
#array('i', [10, 20, 30, 40])
```

Be aware that the new item you add needs to be the same data type as the rest of the items in the array.

Look what happens when I try to add a float to an array of integers:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 to the end of numbers
numbers.append(40.0)
print(numbers)
#output
#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 19, in <module>
# numbers.append(40.0)
#TypeError: 'float' object cannot be interpreted as an integer
```

But what if you want to add more than one value to the end an array?

Use the `extend()`

method, which takes an iterable (such as a list of items) as an argument. Again, make sure that the new items are all the same data type.

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integers 40,50,60 to the end of numbers
#The numbers need to be enclosed in square brackets
numbers.extend([40,50,60])
print(numbers)
#output
#array('i', [10, 20, 30, 40, 50, 60])
```

And what if you don't want to add an item to the end of an array? Use the `insert()`

method, to add an item at a specific position.

The `insert()`

function takes two arguments: the index number of the position the new element will be inserted, and the value of the new element.

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 in the first position
#remember indexing starts at 0
numbers.insert(0,40)
print(numbers)
#output
#array('i', [40, 10, 20, 30])
```

To remove an element from an array, use the `remove()`

method and include the value as an argument to the method.

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
numbers.remove(10)
print(numbers)
#output
#array('i', [20, 30])
```

With `remove()`

, only the first instance of the value you pass as an argument will be removed.

See what happens when there are more than one identical values:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30,10,20])
numbers.remove(10)
print(numbers)
#output
#array('i', [20, 30, 10, 20])
```

Only the first occurence of `10`

is removed.

You can also use the `pop()`

method, and specify the position of the element to be removed:

```
import array as arr
#original array
numbers = arr.array('i',[10,20,30,10,20])
#remove the first instance of 10
numbers.pop(0)
print(numbers)
#output
#array('i', [20, 30, 10, 20])
```

And there you have it - you now know the basics of how to create arrays in Python using the `array module`

. Hopefully you found this guide helpful.

You'll start from the basics and learn in an interacitve and beginner-friendly way. You'll also build five projects at the end to put into practice and help reinforce what you learned.

Thanks for reading and happy coding!

Original article source athttps://www.freecodecamp.org

#python

1598709600

Given two binary arrays **A[]** and **B[]**, of length **N** and **M** respectively, the task is to find the number of rectangles of area **K** consisting of **1**‘s in the matrix **C[][]** generated by multiplying the two arrays such that, **C[i][j] = A[i] * B[j] **( 1 __<__ i __<__ n, 1 __<__ j __<__ m).

**Examples:**

_ N= 3, M = 3, A[] = {1, 1, 0}, B[] = {0, 1, 1}, K = 2_Input:

_ 4_Output:

_ C[][] = {{0, 1, 1}, {0, 1, 1}, {0, 0, 0}}_Explanation:

```
0 1 1 0 1 1 0 1 1 0 1 1
0 1 1 0 1 1 0 1 1 0 1 1
0 0 0 0 0 0 0 0 0 0 0 0
```

Therefore, there are 4 possible rectangles of area 2 from the matrix.

_ N = 4, M = 2, A[] = {0, 0, 1, 1}, B[] = {1, 0, 1}, K = 2_Input:

_ 2_Output:

_ C[][] = {{0, 0, 0}, {0, 0, 0}, {1, 0, 1}, {1, 0, 1}}_Explanation:

```
0 0 0 0 0 0
0 0 0 0 0 0
1 0 1 1 0 1
1 0 1 1 0 1
```

Therefore, there are 2 possible rectangles of area 2 in the matrix.

**Naive Approach: **The simplest approach to solve the problem is to **generate the required matrix** by multiplying the two arrays and for every possible rectangle of area **K, **check if it consists of only 1’s or not…

** Time Complexity:**_ O(N * M * K)_

** Auxiliary Space:**_ O(N * M)_

**Efficient Approach: **To optimize the above approach, the following observations need to be made instead of generating the matrix:

- _The __area of a rectangle is equal to the product of its _
**_length _**_and _*breadth.* - _Using this property, visualize the rectangle as a
which contains only _*submatrix**1**s. Therefore, this submatrix is the result of the product of two subarrays of length a, b where*.*a * b = K* *Since the submatrix contains only*‘s, it is obvious that these two subarrays also contain only*1*‘s in them.*1*

Therefore, the problem reduces to finding the subarrays consisting of only **1**‘s of all possible lengths which are proper divisors of **K**, from the arrays **A[]** and **B[]**. Follow the steps below to solve the problem:

- Precalculate the count of possible subarrays.
- Iterate through all the divisors of
**K**and for each possible pair (**p, q**) where**p * q = K**, check if there exist subarrays of length p, q in A[] and B[]. - Increase the count of possible such subarrays accordingly and finally, print the obtained count.

Below is the implementation of the above approach:

- C++

`// C++ Program to implement`

`// the above approach`

`#include <bits/stdc++.h>`

`**using**`

`**namespace**`

`std;`

`// Function to find the subarrays of`

`// all possible lengths made up of only 1s`

`vector<``**int**``> findSubarrays(vector<``**int**``>& a)`

`{`

`**int**`

`n = a.size();`

`// Stores the frequency`

`// of the subarrays`

`vector<``**int**``> freq(n + 1);`

`**int**`

`count = 0;`

`**for**`

`(``**int**`

`i = 0; i < n; i++) {`

`**if**`

`(a[i] == 0) {`

`// Check if the previous`

`// value was also 0`

`**if**`

`(count == 0)`

`**continue**``;`

`// If the previous value was 1`

`**else**`

`{`

`**int**`

`value = count;`

`**for**`

`(``**int**`

`j = 1; j <= count; j++) {`

`// Find the subarrays of`

`// each size from 1 to count`

`freq[j] += value;`

`value--;`

`}`

`count = 0;`

`}`

`}`

`**else**`

`count++;`

`}`

`// If A[] is of the form ....111`

`**if**`

`(count > 0) {`

`**int**`

`value = count;`

`**for**`

`(``**int**`

`j = 1; j <= count; j++) {`

`freq[j] += value;`

`value--;`

`}`

`}`

`**return**`

`freq;`

`}`

`// Function to find the count`

`// of all possible rectangles`

`**void**`

`countRectangles(vector<``**int**``>& a,`

`vector<``**int**``>& b,`

`**int**`

`K)`

`{`

`// Size of each of the arrays`

`**int**`

`n = a.size();`

`**int**`

`m = b.size();`

`// Stores the count of subarrays`

`// of each size consisting of`

`// only 1s from array A[]`

`vector<``**int**``> subA`

`= findSubarrays(a);`

`// Stores the count of subarrays`

`// of each size consisting of`

`// only 1s from array B[]`

`vector<``**int**``> subB`

`= findSubarrays(b);`

`**int**`

`total = 0;`

`// Iterating over all subarrays`

`// consisting of only 1s in A[]`

`**for**`

`(``**int**`

`i = 1; i < subA.size(); i++) {`

`// If i is a factor of K, then`

`// there is a subarray of size K/i in B[]`

`**if**`

`(K % i == 0 and (K / i) <= m) {`

`total = total + subA[i] * subB[K / i];`

`}`

`}`

`cout << total;`

`}`

`// Driver Code`

`**int**`

`main()`

`{`

`vector<``**int**``> a = { 0, 0, 1, 1 };`

`vector<``**int**``> b = { 1, 0, 1 };`

`**int**`

`K = 2;`

`countRectangles(a, b, K);`

`**return**`

`0;`

`}`

**Output:**

```
2
```

** Time Complexity:**_ O(D) * O(N + M), where D is the number of divisors of K._

** Auxiliary Space:**_ O(N + M)_

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the **DSA Self Paced Course** at a student-friendly price and become industry ready.

#arrays #geometric #mathematical #matrix #searching #area-volume-programs #binary-representation #square-rectangle #subarray #submatrix

1652250166

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#mlm_plan #Binary_mlm #binary_mlm_plan #Binary_mlm_wordpress_plugin #Binary_mlm_woo-commerce #binary_mlm_ecommerce #binary_mlm_software #binary_mlm_wp_plugin #biary_mlm_ecommerce #mlm_plan

1623911281

Printing an array is a quick way to give us visibility on the values of the contents inside. Sometimes the array values are the desired output of the program.

In this article, we’ll take a look at *how to print an array in Java* using four different ways.

While the “best way” depends on what your program needs to do, we begin with the simplest method for printing and then show more verbose ways to do it.

- Print an Array Using Arrays.toString() and Arrays.deepToString()
- Print an Array Using Java 8 Streams
- Print an Array by Converting to List
- Print an Array Using For Loops
- Converting To List and Using an Iterator

#java #array #how to print an array in java #array in java #print an array in java #print