归并排序（C语言实现）

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>   
typedef int RecType;//要排序元素类型  
void Merge(RecType *R, int low, int m, int high)
{
    //将两个有序的子文件R[low..m)和R[m+1..high]归并成一个有序的子文件R[low..high]  
    int i = low, j = m + 1, p = 0;                //置初始值  
    RecType *R1;                        //R1是局部向量  
    R1 = (RecType *)malloc((high - low + 1)*sizeof(RecType));
    if (!R1)
    {
        return;                         //申请空间失败  
    }

    while (i <= m&&j <= high)                //两子文件非空时取其小者输出到R1[p]上  
    {
        R1[p++] = (R[i] <= R[j]) ? R[i++] : R[j++];
    }

    while (i <= m)                         //若第1个子文件非空，则复制剩余记录到R1中  
    {
        R1[p++] = R[i++];
    }
    while (j <= high)                      //若第2个子文件非空，则复制剩余记录到R1中  
    {
        R1[p++] = R[j++];
    }

    for (p = 0, i = low; i <= high; p++, i++)
    {
        R[i] = R1[p];                     //归并完成后将结果复制回R[low..high]  
    }
}

void MergeSort(RecType R[], int low, int high)
{
    //用分治法对R[low..high]进行二路归并排序  
    int mid;
    if (low<high)
    {   //区间长度大于1   
        mid = (low + high) / 2;               //分解  
        MergeSort(R, low, mid);           //递归地对R[low..mid]排序  
        MergeSort(R, mid + 1, high);        //递归地对R[mid+1..high]排序  
        Merge(R, low, mid, high);          //组合，将两个有序区归并为一个有序区  
    }
}
void main()
{
    int a[7] = { 49, 38, 65, 97, 76, 13, 27 }; //这里对7个元素进行排序  
    int low = 0, high = 6;                   //初始化low和high的值  

    printf("Before merge sort: \n");
    for (int i = low; i <= high; i++)
    {
        printf("%d ", a[i]);             //输出测试  
    }
    printf("\n");

    MergeSort(a, low, high);

    printf("\n After merge sort: \n");
    for (int i = low; i <= high; i++)
    {
        printf("%d ", a[i]);             //输出测试  
    }
    printf("\n");
}