(数学) bzoj 1800

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
int tot,n,dist[25],ans;
int main()
{
    int x;
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&x);
        dist[i]=dist[i-1]+x;
        tot+=x;
    }
    for(int a=1;a<=n;a++)
    {
        for(int b=a+1;b<=n;b++)
        {
            for(int c=b+1;c<=n;c++)
            {
                for(int d=c+1;d<=n;d++)
                {
                    if(dist[b]-dist[a]==dist[d]-dist[c]&&tot-dist[d]+dist[a]==dist[c]-dist[b])
                        ans++;
                }
            }
        }
    }
    printf("%d\n",ans);
    return 0;
}