归并排序代码（略）

#include<time.h>
#include<iostream>
#include<string.h>
using namespace std;
void show(int a[], int length) {
  for (int i = 1; i <= length; i++) {
    if (a[i] != 0)
      cout << a[i] << " ";
  }
  cout << endl;
}

/*整体思想：
假设初始序列有N个记录，则可以看成是n个有序的子序列,每个子序列是1个长度，然后两两相互合……，如此往复得到一个N的序列
*/
//算法第一步:相邻2个有序子序列的归并
/*
设2个有序表存放在同一数组中相邻的位置上：R[low...mid]和R[mid+1...high]，每次从2个表中取出一个记录进行关键字的比较，将最小的放入T[]中，
重复，知道其中一个的表位空，然后把剩下的部分直接赋值到T中
*/
int changeTime = 0, compareTime = 0;
void Merge(int R[], int T[], int low, int mid, int high) {//每次归并，需要调用至多n/2*h次算法，（h为每个子序列长度)
  int i = low, j = mid + 1, k = low;
  //表的2半段都非空
  while (i <= mid && j <= high) {
    if (R[i] <= R[j]) {
      T[k++] = R[i++];
    }
    else
      T[k++] = R[j++];
    changeTime++;
    compareTime++;
  }
  while (i <= mid) { T[k++] = R[i++]; changeTime++; }//左边还存在值
  while (j <= high) { T[k++] = R[j++]; changeTime++; }//右边存在值
}

//归并排序调用递归
/*
(1)将当前序列一分为二，找出分裂点
（2）对于左子序列递归归并排序，放入S[low,mid]中
(3)对于子序列R[mid+1,high]递归，进行归并排序，放入S[mid+1,high]中
（4）调用Merge函数把S都前面和后面归并成一个有序的序列
*/

void MSort(int R[], int T[], int low, int high) {
  int S[17] = { 0 };
  if (low == high) T[low] = R[high];
  else {
    int mid = (low + high) / 2;//对当前的序列一分为二，求分裂点
    MSort(R, S, low, mid);//对low-mid递归排序
    MSort(R, S, mid + 1, high);//对mid+1 ->high递归排序
    Merge(S, T, low, mid, high);//将排好序归并到T中
    show(T, 16);
  }
}
//算法分析
/*
（1）时间复杂度 O(n*log2n)
(2）空间复杂度 O(N)需要辅助数组
特点：稳定排序
  可以用于链式结构，递归实现时需要开辟相应的递归工作栈
*/

int main() {
  int *a = new int[17];
  int *b = new int[17];
  int length = 16;
  srand(unsigned(time(0)));
  memset(a, 0, sizeof(a));
  for (int i = 1; i <= 16; i++) {
    a[i] = rand() % 90 + 10;
  }
  cout << "==============" << endl;
  cout << "归并排序:" << endl;
  cout << "==============" << endl;
  cout << "before sort：" << ends;
  for (int i = 1; i <= 16; i++) {
    cout << a[i] << " ";
  }
  cout << endl;
  MSort(a, b, 1, 16);
  cout << "after sort：" << ends;
  for (int i = 1; i <= 16; i++) {
    cout << b[i] << " ";
  }
  cout << endl;
  cout << "changTime=" << changeTime << ",compareTime=" << compareTime << endl;
  delete a;
  a = NULL;
  delete b;
  b = NULL;
}