Problem:
Score : 100 points

Problem Statement

You are given a 4-character string S consisting of uppercase English letters.
Determine if S consists of exactly two kinds of characters which both appear twice in S.

Constraints

The length of S is 4.

S consists of uppercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If S consists of exactly two kinds of characters which both appear twice in S, print Yes; otherwise, print No.

Sample Input 1

ASSA

Sample Output 1

Yes

S consists of A and S which both appear twice in S.

Sample Input 2

STOP

Sample Output 2

No

Sample Input 3

FFEE

Sample Output 3

Yes

Sample Input 4

FREE

Sample Output 4

No

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::io;
use std::str::FromStr;
use std::collections::HashMap;

fn input<T:FromStr>() -> T {
    let mut line: String = String::new();
    io::stdin().read_line(&mut line);
    line.trim().parse().ok().unwrap()
}

fn main() {
    let s: String = input();
    let vec: Vec<char> = s.chars().collect();
    if vec[0] == vec[1] && vec[1] == vec[2] && vec[2] == vec[3] {
        println!("No");
        return;
    }
    if vec[0] == vec[1] {
        if vec[2] == vec[3] {
            println!("Yes");
            return;
        }
    }
    if vec[0] == vec[2] {
        if vec[1] == vec[3] {
            println!("Yes");
            return;
        }
    }
    if vec[0] == vec[3] {
        if vec[1] == vec[2] {
            println!("Yes");
            return;
        }
    }
    println!("No");
}