归并排序

#include <iostream>            //递归
using namespace std;
int n,list[200],temp[200];
void merge_sort(int beg,int end)
{
    if(end==beg)
        return ;
    int mid=(beg+end)/2;
    merge_sort(beg,mid);
    merge_sort(mid+1,end);
    int p=beg,q=mid+1,t=beg;
    while(p<=mid||q<=end)
    {
        if(q>end||(p<=mid&&list[p]<list[q]))
            temp[t++]=list[p++];
        else
            temp[t++]=list[q++];
    }
    for(int i=beg;i<=end;++i)
    {
        list[i]=temp[i];
    }
}
int main()
{
    cin>>n;
    for(int i=0;i<n;++i)
        cin>>list[i];
    merge_sort(0,n-1);
    for(int i=0;i<n;++i)
        cout<<list[i]<<" ";
    cout<<endl;
    return 0;
}

　　

//POJ 2299 Ultra-QuickSort

#include <iostream>        //求归并排序的逆序数
using namespace std;
__int64 list[500005],temp[500005],amount;
int n;
void merge_sort(int beg,int end)
{
    if(end==beg)
        return ;
    int mid=(beg+end)/2;
    merge_sort(beg,mid);
    merge_sort(mid+1,end);
    int p=beg,q=mid+1,t=beg;
    while(p<=mid||q<=end)
    {
        if(q>end||(p<=mid&&list[p]<list[q]))
            temp[t++]=list[p++];
        else
        {
            temp[t++]=list[q++];
            amount+=mid-p+1;
        }
    }
    for(int i=beg;i<=end;++i)
    {
        list[i]=temp[i];
    }
}
int main()
{
    while(cin>>n&&n)
    {
        amount=0;
        for(int i=0;i<n;++i)
            scanf("%I64d",&list[i]);
        merge_sort(0,n-1);
        printf("%I64d\n",amount);
    }
    return 0;
}