【排序算法】归并排序 Java实现

public static void mergeSort(int[] arr, int l, int r) {

    if (r <= l) return;
    int m = (l + r) / 2;

	//分别对左右两组排序
    mergeSort(arr, l, m);
    mergeSort(arr, m + 1, r);

	//合并
    merge(arr, l, r);

}

static void merge(int[] arr, int l, int r) {

    int m = (l + r) / 2;
    int[] tmp = new int[r - l + 1];
    int i = l, j = m + 1, k = 0;
    while (i <= m && j <= r)
        tmp[k ++] = arr[i] <= arr[j] ? arr[i ++] : arr[j ++];
    while (i <= m) tmp[k ++] = arr[i ++];
    while (j <= r) tmp[k ++] = arr[j ++];
    for (i = l, k = 0; i <= r; ++i, ++k)
        arr[i] = tmp[k];

}