RECUR31 - Editorial

editorial
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Problem Link - Interleaving String in Recursion

Problem Statement:

Given three strings s1, s2, and s3, write a recursive function to determine if s3 can be obtained by interleaving s1 and s2. An interleaving of two strings s1 and s2 is a configuration where they are merged in such a way that maintains the left-to-right order of characters from each string.

Approach:

  • Base Case:
    • If s1, s2, and s3 are all empty, return true. This means that we have successfully interleaved all characters from s1 and s2 to form s3.
    • If s3 is empty but either s1 or s2 still has characters, return false. This means we couldn’t completely interleave s1 and s2 to form s3.
  • Recursive Case:
    • Check the first character of s1 with the first character of s3. If they match, recursively check the remaining parts of s1, s3, and s2.
    • Similarly, check the first character of s2 with s3. If they match, recursively check the remaining parts of s2, s3, and s1.
    • If either recursive call returns true, we have found a valid interleaving.

Complexity:

  • Time Complexity: For strings of length n, this approach can have an exponential time complexity, approximately O(2^n) in the worst case because each recursive call has two possible branches (one for s1 and one for s2).
  • Space Complexity: The space complexity is O(n) due to the depth of the recursive call stack.