mergesort實踐

#include <stdio.h>
#include <stdlib.h>

void mergesort(int arr[],int n,int m)
{
    if(n>=m)
    {
        return;
    }
    mergesort(arr,n,(n+m)/2);
    mergesort(arr,(n+m)/2+1,m);
    int mid=(n+m)/2+1,i,k,index;
    int reg[m-n+1];
    for(i=n,k=mid,index=0;i<=mid-1&&k<=m;)
    {
        reg[index++]=arr[i]<arr[k]? arr[i++]:arr[k++];
    }
    while(i<=mid-1)
    {
        reg[index++]=arr[i++];
    }
    while(k<=m)
    {
        reg[index++]=arr[k++];
    }
    for(i=n;i<=m;i++)
    {
        arr[i]=reg[i-n];
    }
    return;
}

int main()
{
    int i,k;
    int arr[10]={13,36,78,9,53,78,100,66,10,14};
    for(i=0;i<10;i++)
        printf("%d ",arr[i]);
    printf("\n");
    mergesort(arr,0,9);
    for(i=0;i<10;i++)
        printf("%d ",arr[i]);
    return 0;
}