JavaScriptAlgorithms/Sort/MergeSort.html at master · biaodigit/JavaScriptAlgorithms · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    function mergeSort(arr) {
        let len = arr.length
        _mergeSort(arr, 0, len - 1)
        console.log(arr)
    }

    function _merge(arr, l, mid, r) {
        let aux = [];
        for (let i = l; i <= r; i++) {
            aux[i - l] = arr[i]
        }
        let i = l,
            j = mid + 1;
        //i=6,mid=7,j=8,l=6,r=9
        //[1,6,5,7]
        for (let k = l; k <= r; k++) {
            if (i > mid) {
                arr[k] = aux[j - l];
                j++
            } else if (j > r) {
                arr[k] = aux[i - l];
                i++
            } else if (aux[i - l] > aux[j - l]) {
                arr[k] = aux[j - l];
                j++
            } else {
                arr[k] = aux[i - l];
                i++
            }
        }
    }

    /**
     * 递归方式
     * @param arr
     * @param l
     * @param r
     * @private
     */
    function _mergeSort(arr, l, r) {
        if (l >= r) {
            return
        }
        let mid = (l + r) >> 1;
        _mergeSort(arr, l, mid);
        _mergeSort(arr, mid + 1, r);
        if (arr[mid] > arr[mid + 1])
            _merge(arr, l, mid, r)
    }

    /**
     * 非递归方式
     * @param arr
     * @param l
     * @param r
     * @private
     */
    function nonRecMergeSort(arr) {
        var stack = [],
            res = [],
            start = 0,
            end = arr.length - 1;
        if (start < end) {
            stack.push(end)
            stack.push(start)
            res.push(end)
            res.push(start)
            while (stack.length) {
                var l = stack.pop()
                var r = stack.pop()
                var mid = l + Math.floor((r - l) / 2)
                if (mid + 1 < r) {
                    stack.push(r)
                    res.push(r)
                    stack.push(mid + 1)
                    res.push(mid + 1)
                }
                if (l < mid) {
                    stack.push(mid)
                    res.push(mid)
                    stack.push(l)
                    res.push(l)

                }
            }
        }
        while (res.length) {
            var ls = res.pop()
            var rs = res.pop()
            var mids = ls + Math.floor((rs - ls) / 2)
            _merge(arr, ls, mids, rs)
        }
        console.log(arr)
    }


    mergeSort([3, 1, 5, 7, 2, 4, 9, 6, 10, 8])
    nonRecMergeSort([3, 1, 5, 7, 2, 4, 9, 11, 6, 12, 10, 8])
</script>
</body>
</html>