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Sum of Digits of String After Convert

Difficulty: Easy

Problem Description

You are given a string s consisting of lowercase English letters, and an integer k. Your task is to convert the string into an integer by a special process, and then transform it by summing its digits repeatedly k times. The conversion involves replacing each letter with its position in the alphabet, and the transformation involves summing the digits of the resulting integer.

Key Insights

  • Each letter in the string corresponds to its position in the alphabet (a=1, b=2, ..., z=26).
  • The conversion from string to integer involves concatenating these positional values.
  • The transformation involves summing the digits of the integer, and this process is repeated k times.
  • The constraints are manageable, allowing for straightforward implementation of the conversion and transformation.

Space and Time Complexity

Time Complexity: O(n + k * m), where n is the length of the string, and m is the number of digits in the number after conversion. Space Complexity: O(1), as we only use a constant amount of space for variables.

Solution

To solve the problem, we will follow these steps:

  1. Convert the string s into an integer by replacing each character with its corresponding position in the alphabet.
  2. Sum the digits of the resulting integer.
  3. Repeat the digit summation process k times.

The algorithm will utilize basic string manipulation and arithmetic operations. The resulting integer after k transformations will be returned.

Code Solutions

def get_sum_of_digits(s: str, k: int) -> int:
    # Step 1: Convert the string to an integer by replacing each letter with its position in the alphabet
    num = ''.join(str(ord(char) - ord('a') + 1) for char in s)
    
    # Convert the concatenated string to an integer
    total = int(num)
    
    # Step 2: Transform the integer k times
    for _ in range(k):
        total = sum(int(digit) for digit in str(total))
    
    return total
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