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3629. Total Characters in String After Transformations I

My accepted Python solution to LeetCode problem 3629, Total Characters in String After Transformations I, running in 6071ms.

  • Difficulty: Medium
  • Python
  • Runtime 6071ms
  • Memory 18.4MB

Read the problem on LeetCode View on GitHub

The problem statement is LeetCode’s and stays on their site. What follows is my accepted solution.

Python

Accepted on LeetCode — runtime 6071ms, memory 18.4MB, accepted 2025-12-29.

python
class Solution:
    def lengthAfterTransformations(self, s: str, t: int) -> int:
        MOD = 10**9 + 7
        
        # Count frequency of each character
        freq = [0] * 26
        for c in s:
            freq[ord(c) - ord('a')] += 1
        
        # Perform t transformations
        for _ in range(t):
            new_freq = [0] * 26
            for i in range(26):
                if freq[i] > 0:
                    if i == 25:  # 'z' -> 'ab'
                        new_freq[0] = (new_freq[0] + freq[i]) % MOD
                        new_freq[1] = (new_freq[1] + freq[i]) % MOD
                    else:  # other chars -> next char
                        new_freq[i + 1] = (new_freq[i + 1] + freq[i]) % MOD
            freq = new_freq
        
        return sum(freq) % MOD

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