Problem Description
You are given two strings s1 and s2 of equal length consisting of letters "x" and "y" only. Your task is to make these two strings equal to each other. You can swap any two characters that belong to different strings, which means: swap s1[i] and s2[j].
Return the minimum number of swaps required to make s1 and s2 equal, or return -1 if it is impossible to do so.
Key Insights
- The strings can only be made equal if the total number of 'x's and 'y's in both strings are the same.
- Swaps can only occur between characters from different strings.
- The number of mismatches between the two strings determines the number of swaps needed.
- Each swap can fix two mismatches.
Space and Time Complexity
Time Complexity: O(n), where n is the length of the strings (since we iterate through the strings to count mismatches). Space Complexity: O(1), as we only use a constant amount of extra space for counting.
Solution
To solve the problem, we will first check if the two strings can be made equal by comparing the counts of 'x' and 'y' in both strings. If they do not match, return -1. If they do, we will count the number of mismatches:
- Count how many 'x's in s1 need to be swapped with 'y's in s2 and vice versa.
- Each swap can fix two mismatched characters, so the total number of swaps required will be the sum of mismatches divided by 2.
We will use simple integer counters to keep track of the mismatches.