0473-matchsticks-to-square.js

function check(arr) {
    let temp = arr[0];
    for (let i = 1; i < arr.length; i++) {
        if (arr[i] !== temp) {
            return false;
        }
    }
    return true;
}

/**
 * @param {number[]} matchsticks
 * @return {boolean}
 */
var makesquare = function (matchsticks) {
    let sides = new Array(4).fill(0),
        ans = false,
        size = 0;

    for (let i = 0; i < matchsticks.length; i++) {
        size += matchsticks[i];
    }
    let max_size = size / 4;
    if (max_size - Math.floor(max_size) !== 0) return false;

    matchsticks = matchsticks.sort((a, b) => b - a);

    function backtrack(i) {
        if (ans) return;
        if (i >= matchsticks.length) {
            if (check(sides)) {
                ans = true;
            }
            return;
        }
        for (let j = 0; j < 4; j++) {
            if (sides[j] + matchsticks[i] > max_size) {
                continue;
            }
            sides[j] += matchsticks[i];

            backtrack(i + 1);
            sides[j] -= matchsticks[i];
        }
    }
    backtrack(0);

    return ans;
};