Python – Kth digit Sum

Given a Numeric list, extract the sum of the Kth digit.

Input : test_list = [5467, 34232, 45456, 22222, 3455], K = 2 
Output : 19 
Explanation : 6 + 2 + 4 + 2 + 5 = 19.

Input : test_list = [5467, 34232, 45456, 22222, 3455], K = 0 
Output : 17 
Explanation : 5 + 3 + 4 + 2 + 3 = 17. 

Method #1 : Using str() + loop

In this, we convert the element to string and then compute the summation of only Kth digit by extracting it using loop.

Output:

The original list is : [5467, 34232, 45456, 22222, 3455]
Kth digit sum : 19

Time Complexity: O(n)
Auxiliary Space: O(n)

Method #2 : Using sum() + list comprehension + str()

In this, we perform the task of getting sum using sum(), and list comprehension is used to get one-liner approach to the problem. 

Output:

The original list is : [5467, 34232, 45456, 22222, 3455]
Kth digit sum : 19

Time Complexity: O(n)
Auxiliary Space: O(n)

Use string slicing to extract the Kth digit from each number:

Approach:

Define a function named “kth_digit_sum” that takes two arguments, a list of integers named “test_list” and an integer named “K”.
Convert each integer in the list to a string using the “str” function and map it to a new list using the “map” function.
Slice the Kth character from each string using string slicing and map it to a new list using the “map” function.
Convert the list of characters to a list of integers using the “map” and “int” functions.
Add up the integers in the list using the “sum” function and return the result.
Use the function to solve the given input and print the output.

19
17

Time complexity: O(n * k), where n is the length of the list and k is the value of K.
Auxiliary Space: O(n * k), because we create a new list for each step of the mapping operation.