We use cookies (including Google cookies) to personalize ads and analyze traffic. By continuing to use our site, you accept our Privacy Policy.

SimplyLeet
TagsDisclaimersPrivacyTermsContactAbout Us

Total Characters in String After Transformations I

Difficulty: Medium

Problem Description

You are given a string s and an integer t, representing the number of transformations to perform. In one transformation, every character in s is replaced according to the following rules:

  • If the character is 'z', replace it with the string "ab".
  • Otherwise, replace it with the next character in the alphabet.

Return the length of the resulting string after exactly t transformations. Since the answer may be very large, return it modulo 10^9 + 7.

Key Insights

  • Each character transformation can significantly increase the length of the string, especially when 'z' is involved.
  • The number of transformations may lead to exponential growth in string size due to the rules defined for 'z'.
  • The problem requires a careful calculation of the length after t transformations without explicitly constructing the transformed string.

Space and Time Complexity

Time Complexity: O(n + t), where n is the length of the string s and t is the number of transformations. Space Complexity: O(1), as we only need a few variables to store lengths and counts.

Solution

To solve the problem, we can iterate through the string and simulate the transformations while keeping track of the length.

  • For each character, we determine how many times it will transform into 'z' and subsequently into "ab", increasing the length accordingly.
  • We utilize a loop to apply transformations t times, adjusting the length based on the rules provided.
  • Finally, we return the length modulo 10^9 + 7.

Code Solutions

def transformed_length(s: str, t: int) -> int:
    MOD = 10**9 + 7
    length = len(s)
    
    for transformation in range(t):
        new_length = 0
        for char in s:
            if char == 'z':
                new_length += 2  # 'z' becomes "ab"
            else:
                new_length += 1  # any other character becomes the next character
            
        length = new_length % MOD
        # Prepare for the next transformation
        s = 'a' * length  # Simplified representation, we don't store the actual string.
    
    return length % MOD
← Back to All Questions