pub fn pangrams(s: &str) -> String {
    //Time complexity: O(n)
    //Space complexity (ignoring input): O(1)
    let mut bit_mask = 0;
    for letter in s.to_lowercase().chars() {
        if ('a'..='z').contains(&letter) {
        let bit_pos = letter as u32 - 'a' as u32;
        bit_mask |= 1 << bit_pos;
        };
    }
    if bit_mask == (1 << 26) - 1 {
        return "pangram".to_string();
    };

    "not pangram".to_string()
}