Make String a Subsequence Using Cyclic Increments

Problem Description

You are given two 0-indexed strings str1 and str2. In an operation, you select a set of indices in str1, and for each index i in the set, increment str1[i] to the next character cyclically. Return true if it is possible to make str2 a subsequence of str1 by performing the operation at most once, and false otherwise.

Key Insights

• A subsequence of a string can be formed by deleting some characters without changing the order of the remaining characters.
• We can increment characters in str1 cyclically, meaning after 'z', it wraps around to 'a'.
• We need to check if it's possible to turn str1 into a sequence that can contain str2 after at most one operation.

Space and Time Complexity

Time Complexity: O(n + m), where n is the length of str1 and m is the length of str2.
Space Complexity: O(1), as we only use a constant amount of extra space.

Solution

To solve this problem, we can use a two-pointer approach. We will iterate through both strings, attempting to match characters from str2 to str1. If a character in str1 is not equal to the current character in str2, we check if we can increment it cyclically to match. If we cannot match any character in str2 after the allowed operation, we return false.

1. Initialize two pointers, one for str1 and one for str2.
2. Loop through str1 and str2 until we exhaust either string.
3. If characters match, move both pointers forward.
4. If they do not match, check if we can increment the character in str1 to match the character in str2.
5. If we reach the end of str2 while successfully matching its characters, return true.

Code Solutions