Leetcode with JS: 2222. Number of Ways to Select Buildings

2222. Number of Ways to Select Buildings.js

var numberOfWays = function(s) {
    /*
        n0 => numnber of substring of 0
        n1 => numnber of substring of 1
        n01 => numnber of substring of 01
        n10 => numnber of substring of 10
        selection must be 101 or 010
    */
    let [n0, n1, n01, n10, ans] = [0, 0, 0, 0, 0]
    for (let i = 0; i < s.length; i++) {
        if (s[i] === '1') {
            ans += n10
            n01 += n0
            n1++
        }
        else {
            ans += n01
            n10 += n1
            n0++
        }
    }
    return ans
};