Count the number of special characters i

Hash Table String

66.7% acceptance

Feb 23, 2026

171

You are given a string word. A letter is called special if it appears both in lowercase and uppercase in word. Return the number of special letters in word.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn number_of_special_chars(word: String) -> i32 {
    let mut lower = [false; 26];
    let mut upper = [false; 26];
    for b in word.bytes() {
      if b.is_ascii_lowercase() {
        lower[(b - b'a') as usize] = true;
      } else {
        upper[(b - b'A') as usize] = true;
      }
    }
    (0..26).filter(|&i| lower[i] && upper[i]).count() as i32
  }
}