合并递归

    1.     function mergeSort(array) {
    2.         if (array.length <= 1) return array
    3.         let mid = Math.floor(array.length / 2)
    4.         let left = array.slice(0, mid)
    5.         let right = array.slice(mid)
    6.         return merge(mergeSort(left), mergeSort(right))
    7.     }
    9.     function merge(a, b) {
    10.         let array
    11.         if (a.length === 0) return b;
    12.         if (b.length === 0) return a;
    13.         if (a[0] < b[0]) {
    14.             array = [a[0]].concat(merge(a.slice(1), b))
    15.         } else {
    16.             array = [b[0]].concat(merge(a, b.slice(1)))
    17.         }
    18.         return array
    19.     }

    合并非递归

        function mergeSort(array) {
        if (array.length <= 1) return array
        let mid = Math.floor(array.length / 2)
        let left = array.slice(0, mid)
        let right = array.slice(mid)
        return merge(mergeSort(left), mergeSort(right))
    }

    function merge(a, b) {
        let i = 0,
            j = 0,
            k = 0,
            array = [];
        while (i < a.length && j < b.length) {
            if (a[i] < b[j]) {
                array[k] = a[i];
                k++;
                i++;
            } else {
                array[k] = b[j];
                k++;
                j++;
            }
        }
        if (i >= a.length) {
            array = array.concat(b.slice(j));
        } else if (j >= b.length) {
            array = array.concat(a.slice(i));
        }
        return array
    }