Learn AI Create the Future — with Pranay
Main site

LeetCode solutions

1873. Longest Nice Substring

My accepted Python solution to LeetCode problem 1873, Longest Nice Substring, running in 0ms.

  • Difficulty: Easy
  • Python
  • Runtime 0ms
  • Memory 17.1MB

Read the problem on LeetCode View on GitHub

The problem statement is LeetCode’s and stays on their site. What follows is my accepted solution.

Python

Accepted on LeetCode — runtime 0ms, memory 17.1MB, accepted 2025-12-29.

python
class Solution:
    def longestNiceSubstring(self, s: str) -> str:
        # Divide and conquer: split on bad chars
        # Time: O(n^2), Space: O(n)
        if len(s) < 2:
            return ""
        
        char_set = set(s)
        for i, c in enumerate(s):
            if c.swapcase() not in char_set:
                # Split at this position
                left = self.longestNiceSubstring(s[:i])
                right = self.longestNiceSubstring(s[i+1:])
                return left if len(left) >= len(right) else right
        
        return s  # Whole string is nice

Source