bzoj1800 飞行棋

//Serene
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cstdio>
#include<cmath>
using namespace std;
const int maxn=20+5;
int n,a[maxn],tot,sum;

int aa;char cc;
int read() {
	aa=0;cc=getchar();
	while(cc<‘0‘||cc>‘9‘) cc=getchar();
	while(cc>=‘0‘&&cc<=‘9‘) aa=aa*10+cc-‘0‘,cc=getchar();
	return aa;
}

int main() {
	n=read();
	for(int i=1;i<=n;++i) a[i]=read(),tot+=a[i];
	if(tot&1) {
		printf("0");
		return 0;
	}
	else tot>>=1;
	int t=0,now=0;
	for(int pos=1;pos<=n;++pos) {
		while(now<tot) {
			t=t%n+1; now+=a[t];
		}
		if(now==tot) sum++;
		now-=a[pos];
	}
	sum/=2;
	printf("%d",sum*(sum-1)/2);
	return 0;
}