How to convert types in Python

How to convert types in Python

Originally published by Vatsal Mistry&nbsp;at&nbsp;<a href="" target="_blank"></a>&nbsp;on&nbsp;Apr 18

Foregone Solution — A problem from Google Code Jam's Qualifier Round this year felt like so easy to code.

You can checkout the full problem description at this LINK.

Problem(Source : Google Code Jam 2019 Website)

Someone just won the Code Jam lottery, and we owe them N jamcoins! However, when we tried to print out an over sized check, we encountered a problem. The value of N, which is an integer, includes at least one digit that is a 4... and the 4 key on the keyboard of our over sized check printer is broken.

Fortunately, we have a workaround: we will send our winner two checks for positive integer amounts A and B, such that neither A nor B contains any digit that is a 4, and A + B = N. Please help us find any pair of values A and B that satisfy these conditions.


While reading out the problem description, I read the input constraints and range which were around 10¹⁰⁰. So it was a bad idea to think of a very straight loop-based solution, that would strike the time complexity showing the nightmarish message “ Time limit Exceeded ! ”.

So I thought of dealing this with the help of strings. Python saved me!

Assuming you’ve read the problem description through the link above, there is a number N which may contain the digit 4 with any number of occurrences. The task was to find out two numbers A and B such that A and B doesn’t contain any occurrence of the digit 4 and summation of A and B should equal N(A+B=N).

So I thought of creating a new number let’s assume A for now, that would be same in length as N(length means number of digits in the number). The idea is while constructing the number A, we would analyze the number N digit by digit. For each occurrence of digit 4 in number N, we would add digit 1 in the number A. For rest of the digits in N, add digit 0 in the A. Following this, I got a number A.

I obtained the other number B by subtracting newly constructed A from N. And you see, I got two numbers A and B that do not contain digit 4 and the summation is equal to N.

For implementing this logic, I could not think of anything, but Python. The easy type conversions from integer to string or string to list and viz made it so easy to achieve this working.



# __author__ = "Vatsal Mistry"
    # A solution for FOREGONE SOLUTION Problem from Qualifier Round of Google's CodeJam 2019.
    # Problem Description Link :

    # Importing regular expression module.
    import re

    # tc holds the number of testcases.
    tc = int(input())

    # A loop over tc i.e. number of testcases.
    for i in range(tc):

        # N holds the input number.
        N = int(input())

        # Converting the integer N into string N_str.
        N_str = str(N)

        # Defining an empty list index_list.
        index_list = list()

        # Looping over N_str for finding the indices of positions where the digit "4" occurs.
        # finditer method from re module is used. It returns the indices where match is found.
        for match in re.finditer("4", N_str): 

            # Adding the indices to the index_list defined above.

        # Creating a new empty list new_number_list. 
        new_number_list = list()

        #The following block is the logic to create a new number with the rules that whereever there occurs a digit 4 in the original number there will be digit 1 in the new number, rest the digit will be 0.
        # Loop to create new number, each digit in list.
        for j in range(len(N_str)):
            if j not in index_list:

        # Converting the new number list into string.
        new_number = int("".join(new_number_list))

        # Defining and assigning as per given condition in problem.
        A = new_number
        B = N - new_number

        # Printing result.
        print("Case #" + str(i+1) + ":" + " " + str(A) + " " + str(B))

My View

This way it cracked all the test cases, no matter how large the input number was!

I believe the same logic can be implemented in various other languages, possibly the best in terms of time would be in C/C++, but Python just makes it super easy. You can switch from different data types with just few keywords and as you want.

I encourage any reader to try out this in some other language or in Python with less lines of code.

*" The joy of coding Python should be in seeing short, concise, readable classes that express a lot of action in a small amount of clear code — not in reams of trivial code that bores the reader to death. "*

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