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 JavaScript (node.js v5.12) (judge verdict: Wrong Answer)

'use strict'
function main(input) {
    const S = input.split("");
    const dict = new Map();
    for (let char of S) {
        if (!dict.has(char)) {
            dict.set(char, 1);
        } else {
            dict.set(char, dict.get(char) + 1);
        }
    }
    const dictArr = Array.from(dict);
    const Nkey = dictArr.map((d) => d[0]).length;
    const counts = dictArr.map((d) => d[1]);
    if (counts.filter((count) => count === 2).length === Nkey) {
        console.log('Yes');
    } else {
        console.log('No');
    }
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));