solution.js

/**
 * @param {number[]} A
 * @return {string}
 */
var largestTimeFromDigits = function (A) {
    // 枚举所有有效(那一堆if else)情况
    function backTracking (list, sequence, used, A) {
        if (list.length === 4) {
            return sequence.push(list.slice());
        }
        for (let i = 0; i < A.length; i++) {
            if (used[i]) {
                continue;
            }

            const len = list.length;
            if (len === 0) {
                if (A[i] > 2) {
                    continue;
                }
            } else if (len === 1) {
                if (list[0] === 2 && A[i] > 3) {
                    continue;
                }
            } else if (len === 2) {
                if (A[i] > 5) {
                    continue;
                }
            }

            used[i] = true;
            list.push(A[i]);
            backTracking(list, sequence, used, A);
            list.pop();
            used[i] = false;
        }
    }
    const sequence = [];
    const used = new Array(4).fill(false);
    backTracking([], sequence, used, A);
    if (sequence.length === 0) {
        return '';
    }
    // 映射为时间
    const time = sequence.map((list) => {
        return (list[0] * 10 + list[1]) * 60 + list[2] * 10 + list[3];
    });
    // 找到对应时间最大的项
    let index = 0;
    let value = time[0];
    for (let i = 1; i < time.length; i++) {
        if (time[i] > value) {
            index = i;
            value = time[i];
        }
    }

    return `${sequence[index][0]}${sequence[index][1]}:${sequence[index][2]}${sequence[index][3]}`;
};