Count Nice Pairs in an Array LeetCode solution in JavaScript

1
const MOD = 1e9 + 7;
2
const countNicePairs = (a) => {
3
  let m = new Map();
4
  let res = 0;
5
  for (const e of a) {
6
    let target = e - rev(e);
7
    let cnt = m.get(target) || 0;
8
    res += cnt;
9
    m.set(target, cnt + 1);
10
  }
11
  return res % MOD;
12
};
13

14
/* Another version
15
const countNicePairs = (a) => {
16
    let m = new Map();
17
    let res = 0;
18
    for (const e of a) {
19
        let target = e - rev(e);
20
        let cnt = m.get(target) + 1 || 1;
21
        m.set(target, cnt);
22
        res += cnt - 1;
23
    }
24
    return res % MOD;
25
};
26
*/
27

28
const rev = (num) => {
29
  let s = num + "";
30
  let res = "";
31
  let n = s.length;
32
  for (let i = n - 1; ~i; i--) res += s[i];
33
  return Number(res);
34
};