笛卡尔乘积的javascript版实现和应用

/*
 * @Author: Mr Jiang.Xu
 * @Date: 2019-08-31 00:05:33
 * @Last Modified by:   Mr Jiang.Xu
 * @Last Modified time: 2019-08-31 00:05:33
 */
function cartesian(arr) {
    if (arr.length < 2) return arr[0] || [];
    return [].reduce.call(arr, function (col, set) {
        let res = [];
        col.forEach(c => {
            set.forEach(s => {
                let t = [].concat(Array.isArray(c) ? c : [c]);
                t.push(s);
                res.push(t);
            })
        });
        return res;
    });
}
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