Longest palindrome

Hash Table String Greedy

55.8% acceptance

Jan 13, 2026

6347

446

Given a string s which consists of lowercase or uppercase letters, return the length of the longest palindrome that can be built with those letters. Letters are case sensitive, for example, "Aa" is not considered a palindrome.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn longest_palindrome(s: String) -> i32 {
    let mut counts = [0; 128];
    for ch in s.bytes() {
      counts[ch as usize] += 1;
    }
    
    let mut length = 0;
    let mut has_odd = false;
    
    for count in counts.iter() {
      if count % 2 == 0 {
        length += count;
      } else {
        length += count - 1;
        has_odd = true;
      }
    }
    
    if has_odd {
      length + 1
    } else {
      length
    }
  }
}