C++归并排序算法实例

#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;
}