This is the blog post version of the
Let’s go straight to the point
Coding Challenge
Create a function that takes an array of numbers between 1 and 10 (excluding one number) and returns the missing number.
A few points:
- The array of numbers will be unsorted (not in order).
- Only one number will be missing.
Examples
Ruby
1
find_missing_num([1, 2, 3, 4, 6, 7, 8, 9, 10]) ➞ 5
2
3
find_missing_num([7, 2, 3, 6, 5, 9, 1, 4, 8]) ➞ 10
4
5
find_missing_num([10, 5, 1, 2, 4, 6, 8, 3, 9]) ➞ 7
Pretty simple, isn’t it?
Algorithm in Ruby
Let’s break the algorithm down to a few small steps:
Step 1
We need to go through a list of items (an array), going from 1 to 10.
Ruby
1
def find_missing_num(array)
2
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10].each do |item|
3
end
4
end
5
6
array = [1, 2, 3, 4, 6, 7, 8, 9, 10]
7
find_missing_num(array)
Ruby provides us a really better way to do this:
Ruby
1
def find_missing_num(array)
2
(1..10).each do |item|
3
end
4
end
5
6
array = [1, 2, 3, 4, 6, 7, 8, 9, 10]
7
find_missing_num(array)
Step 2
We’re going to compare each number (from 1 to 10) with the numbers in the given array.
Ruby
1
def find_missing_num(array)
2
(1..10).each do |item|
3
array.each do |number|
4
if item == number
5
break # breaking the execution
6
end
7
end
8
end
9
end
10
11
array = [1, 2, 3, 4, 6, 7, 8, 9, 10]
12
find_missing_num(array)
We break the execution once if find the desired number because we don’t need to continue looking for the number
Step 3
Because we want to return the number that wasn’t found in the array, I’m going to create a local variable to indicate that.
Ruby
1
def find_missing_num(array)
2
(1..10).each do |item|
3
found = false
4
array.each do |number|
5
if item == number
6
found = true
7
break
8
end
9
end
10
if found = false
11
return item
12
end
13
end
14
end
15
16
array = [1, 2, 3, 4, 6, 7, 8, 9, 10]
17
find_missing_num(array)
That’s it!
I know, that’s not beautiful but it works : )
Do you have a better/different version? Drop that in the comments and bring more healthy discussions :)
Thanks for the visit and in the next coding challenge we’re going to explore a more decent way to solve this puzzle, see you there!
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