#include<iostream>using namespace std;void Merge(int* arr,int left,int right,int mid, int*& tmparr)
{int begin1 = left, end1 = mid;int begin2 = mid + 1, end2 = right;int tmpi = left;//下面合并两个数组为一个有序数组（升序）；while (begin1<=end1&&begin2<=end2){if (arr[begin1] < arr[begin2]){tmparr[tmpi++] = arr[begin1++];}else if (arr[begin1] >= arr[begin2]){tmparr[tmpi++] = arr[begin2++];}}while (begin1<=end1){tmparr[tmpi++] = arr[begin1++];}while (begin2 <= end2){tmparr[tmpi++] = arr[begin2++];}//每次子数组排序好都必须拷贝到原数组，使原数组越来越接近有序。如果被分割的子数组都不有序，那么合并成的大数组也一定不会有序。memcpy(arr+left, tmparr+left, sizeof(int)*(right-left+1));
}//时间复杂度O（N*logN），空间复杂度O（N）；
void Merge_Sort(int* arr,int left,int right,int*& tmparr)
{if (left >= right) return;int mid = (left + right) / 2;Merge_Sort(arr,left,mid,tmparr);Merge_Sort(arr, mid+1, right,tmparr);Merge(arr,left,right,mid,tmparr);
}int main()
{int arr[] = {66,72,53,41,38,39,25,40,90};int size = sizeof(arr) / sizeof(int);int* tmparr = new int[size];//构建一个一模一样一样的数组,这也就是空间复杂度O（N）的原因；Merge_Sort(arr,0,size-1,tmparr);delete []tmparr;for (auto& e:arr){cout<<e<<" ";}return 0;
}