题解 | #字符个数统计#

//和上一个题一样 但不用反转
use std::io::{self, *};

fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    let mut res = String::new();
    for c in s.trim().chars() {
        if !res.contains(c) {
            res.push(c)
        }
    }
    println!("{}", res.len());
}