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Longest Uncommon Subsequence I

Difficulty: Easy

Problem Description

Given two strings a and b, return the length of the longest uncommon subsequence between a and b. If no such uncommon subsequence exists, return -1. An uncommon subsequence between two strings is a string that is a subsequence of exactly one of them.

Key Insights

  • An uncommon subsequence is defined as a subsequence that appears in one string but not in the other.
  • If both strings are equal, every subsequence of one is also a subsequence of the other, resulting in -1.
  • If the strings are different, the longer string itself is the longest uncommon subsequence.

Space and Time Complexity

Time Complexity: O(n) where n is the length of the longer string.
Space Complexity: O(1) since we are only using a constant amount of extra space.

Solution

To solve this problem, we need to compare the two strings:

  1. Check if the two strings are equal. If they are, return -1.
  2. If they are not equal, the length of the longest uncommon subsequence is simply the length of the longer string. This approach works because if one string is not a subsequence of the other, the longer string itself serves as the longest uncommon subsequence.

Code Solutions

def findLUSlength(a: str, b: str) -> int:
    # If both strings are the same, return -1
    if a == b:
        return -1
    # Return the length of the longer string
    return max(len(a), len(b))
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