How do you solve Longest Uncommon Subsequence I on LeetCode?

Longest Uncommon Subsequence I (LeetCode #521) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(1) space complexity. Key insight: If the two strings are equal, there are no uncommon subsequences.

What is the brute force solution for Longest Uncommon Subsequence I?

The brute force approach for Longest Uncommon Subsequence I is Brute Force, with O(n²) time complexity and O(2^n) space complexity. The brute-force approach checks all possible subsequences of both strings to find the longest one that is unique to either string. This method is straightforward but inefficient. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Longest Uncommon Subsequence I?

Longest Uncommon Subsequence I uses the following concepts: String. The recommended patterns to study are: String comparison, Dynamic programming (for more complex subsequence problems).

What are the interview tips for Longest Uncommon Subsequence I?

Always consider edge cases, such as when the two strings are the same. Think about the properties of subsequences and how they relate to the problem. Communicate your thought process clearly, especially when transitioning from brute-force to optimal solutions.

What are common mistakes when solving Longest Uncommon Subsequence I?

Failing to check if the strings are equal before proceeding. Overcomplicating the problem by trying to generate subsequences instead of leveraging string properties.

#521

Longest Uncommon Subsequence I

Easy

StringString comparisonDynamic programming (for more complex subsequence problems)

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(2^n)	O(1)

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Intuition

Time O(n)Space O(1)

The optimal solution leverages the fact that if the two strings are equal, there are no uncommon subsequences. If they are different, the longer string itself is the longest uncommon subsequence.

⚙️

Algorithm

3 steps

1Step 1: Check if strings a and b are equal.
2Step 2: If they are equal, return -1.
3Step 3: If they are not equal, return the length of the longer string.

solution.py6 lines

1# Full working Python code
2
3def longest_uncommon_subsequence(a, b):
4    if a == b:
5        return -1
6    return max(len(a), len(b))

ℹ

Complexity note: The time complexity is O(n) due to the string comparison and length calculation, while the space complexity is O(1) since we are not using any additional data structures.

1If the two strings are equal, there are no uncommon subsequences.
2The longest uncommon subsequence is simply the longer of the two strings if they are different.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.