Make the string great

String Stack

68.4% acceptance

Feb 25, 2026

3218

186

Given a string s of lower and upper case English letters. A good string is a string which doesn't have two adjacent characters s[i] and s[i + 1] where s[i] is a lower-case letter and s[i + 1] is the same letter but in upper-case or vice-versa. To make the string good, you can choose two adjacent characters that make the string bad and remove them. Return the string after making it good.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn make_good(s: String) -> String {
    let mut stack: Vec<u8> = Vec::new();
    for b in s.bytes() {
      if let Some(&top) = stack.last() {
        // They're the same letter but different case if their difference is 32
        if top != b && top.to_ascii_lowercase() == b.to_ascii_lowercase() {
          stack.pop();
          continue;
        }
      }
      stack.push(b);
    }
    String::from_utf8(stack).unwrap()
  }
}