Largest substring between two equal characters

Hash Table String

68.3% acceptance

Feb 25, 2026

1407

Given a string s, return the length of the longest substring between two equal characters, excluding the two characters. If there is no such substring return -1. A substring is a contiguous sequence of characters within a string.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn max_length_between_equal_characters(s: String) -> i32 {
    let s: Vec<u8> = s.bytes().collect();
    let mut first = [usize::MAX; 26];
    let mut ans = -1i32;
    for (i, &c) in s.iter().enumerate() {
      let idx = (c - b'a') as usize;
      if first[idx] == usize::MAX {
        first[idx] = i;
      } else {
        ans = ans.max(i as i32 - first[idx] as i32 - 1);
      }
    }
    ans
  }
}