#include <iostream> using namespace std;   //将有二个有序数列a[first...mid]和a[mid...last]合并。 void mergearray(int a[], int first, int mid, int last, int temp[]) {      int i = first, j = mid + 1;      int m = mid,   n = last;      int k = 0;        while (i <= m && j <= n)      {           if (a[i] <= a[j])                temp[k++] = a[i++];           else                temp[k++] = a[j++];      }        while (i <= m)           temp[k++] = a[i++];        while (j <= n)           temp[k++] = a[j++];        for (i = 0; i < k; i++)           a[first + i] = temp[i]; } void mergesort(int a[], int first, int last, int temp[]) {      if (first < last)      {           int mid = (first + last) / 2;           mergesort(a, first, mid, temp);    //左边有序           mergesort(a, mid + 1, last, temp); //右边有序           mergearray(a, first, mid, last, temp); //再将二个有序数列合并      } }   bool MergeSort(int a[], int n) {      int *p = new int[n];      if (p == NULL)           return false;      mergesort(a, 0, n - 1, p);      delete[] p;      return true; }   int main() {      int arr[] = {2, 1, 4};      MergeSort(arr, 3);        for (int i = 0; i < 3; ++i)      {           cout<<arr[i]<<" ";      }      cout<<endl; }