17.6归并排序原理及实战

#include <stdio.h>
#include <stdlib.h>
#define N 7
typedef int ElemType;

void Merge(ElemType A[],int low,int mid,int high)
{
    static ElemType B[N];    //加static的目的是无论函数执行多少次，都只有一个B[N]
    int i,j,k;
    for (i  = low;  i <= high; i++) {
        //把A[i]里的元素都给B[i]
        B[i]=A[i];
    }
    k=low;
    for (i = low, j = mid+1; i<=mid&&j<=high;) {   //合并两个有序数组
        if(B[i]<B[j])
        {
            A[k]=B[i];
            i++;
            k++;
        } else{
            A[k]=B[j];
            j++;
            k++;
        }
    }
    //把某一个有序数组中剩余的元素放进来
    while (i<=mid)   //前一半有剩余的放入
    {
        A[k]=B[i];
        i++;
        k++;
    }
    while (j<=high)    //后一半有剩余的放入
    {
        A[k]=B[j];
        j++;
        k++;
    }
}
//归并排序不限制是两两归并，还是多个归并，考研是两两归并
void MergeSort(ElemType A[],int low,int high)  //递归分割
{
    if(low<high)
    {
        int mid=(low+high)/2;
        MergeSort(A,low,mid);   //排序好前一半
        MergeSort(A,mid+1,high);   //排序好后一半
        Merge(A,low,mid,high);     //让两个排序好的数组合并
    }
}

//打印
void print(int* a)
{
    for (int i = 0; i < N; i++) {
        printf("%3d",a[i]);
    }
    printf("\n");
}
int main() {
    int A[N]={49,38,65,97,76,13,27};   //数组，7个元素
    MergeSort(A,0,6);
    print(A);
    return 0;
}