Reverse only letters

Two Pointers String

68.2% acceptance

Feb 25, 2026

2438

Given a string s, reverse the string according to the following rules: All the characters that are not English letters remain in the same position. All the English letters (lowercase or uppercase) should be reversed. Return s after reversing it.

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn reverse_only_letters(s: String) -> String {
    let mut chars: Vec<char> = s.chars().collect();
    let (mut l, mut r) = (0, chars.len() - 1);
    while l < r {
      while l < r && !chars[l].is_alphabetic() { l += 1; }
      while l < r && !chars[r].is_alphabetic() { if r == 0 { break; } r -= 1; }
      if l < r { chars.swap(l, r); l += 1; if r > 0 { r -= 1; } }
    }
    chars.iter().collect()
  }
}