分治思想

//歸併
    void Merge(int R[],int left,int right)
    {
        int mid=(left+right)/2;
        int *p=(int *) malloc(sizeof(int)*(right-left+1));
        int i=left,j=mid+1;
        int k=0;
        while(i<=mid&&j<=right){
            if(R[i]>R[j]){
                p[k++]=R[j++];
            }else{
                p[k++]=R[i++];
            }
        }
        while(i<=mid)
            p[k++]=R[i++];
        while(j<=right)
            p[k++]=R[j++];
        k=0;
        while(left<=right){
            R[left++]=p[k++];
        }
        free(p);
    }
    
    
    //歸併排序
    void MergeSort(int R[],int left,int right)
    {
        if(left<right){
            int mid=(left+right)/2;
            MergeSort(R,left,mid);
            MergeSort(R,mid+1,right);
            Merge(R,left,right);
        }
    }