Longest nice substring

Hash Table String Divide and Conquer Bit Manipulation Sliding Window

63.8% acceptance

Feb 25, 2026

1506

973

A string s is nice if, for every letter of the alphabet that s contains, it appears both in uppercase and lowercase. Given a string s, return the longest substring of s that is nice. If there are multiple, return the substring of the earliest occurrence. If there are none, return an empty string.

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn longest_nice_substring(s: String) -> String {
    let s = s.as_bytes();
    let n = s.len();
    let mut best_start = 0;
    let mut best_len = 0;
    for i in 0..n {
      let mut lower = 0u32;
      let mut upper = 0u32;
      for j in i..n {
        let c = s[j];
        if c.is_ascii_lowercase() {
          lower |= 1 << (c - b'a');
        } else {
          upper |= 1 << (c - b'A');
        }
        if lower == upper && j - i + 1 > best_len {
          best_len = j - i + 1;
          best_start = i;
        }
      }
    }
    String::from_utf8(s[best_start..best_start + best_len].to_vec()).unwrap()
  }
}