java实现归并排序算法

public static void mergeSort(int[] a, int[] tmp, int left, int right) {    if (left < right) {      int mid = left + (right - left) / 2;      mergeSort(a, tmp, left, mid);// 左排序      mergeSort(a, tmp, mid + 1, right);// 右排序      merge(a, tmp, left, mid + 1, right);// 左右合并    }  }public static void merge(int[] a, int[] tmp, int left, int rightPos,      int right) {    int leftEnd = rightPos - 1;    int tmpPos = left;    int num = right - left + 1;    while (left <= leftEnd && rightPos <= right) {      if (a[left] < a[rightPos]) {        tmp[tmpPos++] = a[left++];      } else {        tmp[tmpPos++] = a[rightPos++];      }    }    while (left <= leftEnd) {      tmp[tmpPos++] = a[left++];    }    while (rightPos <= right) {      tmp[tmpPos++] = a[rightPos++];    }    for (int i = 0; i < num; i++, right--) {      a[right] = tmp[right];    }  }