bzoj1800: [Ahoi2009]fly 飞行棋

#include<cstdio>
#include<cstring>
#include<cctype>
#include<algorithm>
using namespace std;
#define rep(i,s,t) for(int i=s;i<=t;i++)
#define dwn(i,s,t) for(int i=s;i>=t;i--)
#define clr(x,c) memset(x,c,sizeof(x))
int read(){
    int x=0;char c=getchar();
    while(!isdigit(c)) c=getchar();
    while(isdigit(c)) x=x*10+c-‘0‘,c=getchar();
    return x;
}
const int nmax=25;
int a[nmax];
int main(){
    int n=read(),sum=0;
    rep(i,1,n) a[i]=read(),sum+=a[i];
    if(sum%2) {
        printf("0\n");return 0;
    }
    int cur=1,ans=0,tot=0;sum>>=1;
    rep(i,1,n-1){
        tot+=a[i];
        while(tot>sum) tot-=a[cur++];
        if(tot==sum) ans++;
    }
    printf("%d\n",ans*(ans-1)>>1);
    return 0;
}