2007-2008 Winter Petrozavodsk Camp, Andrew Stankevich Contest 28 (ASC 28)J. Triatrip（bitset优化）

https://codeforc.es/gym/100342

bitset存边搞一搞

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=2e3+5;
bitset<N>in[N],out[N],t;
char s[N][N];
int n;
int main(){
    freopen("triatrip.in","r",stdin);//没这两行就wa 服了
    freopen("triatrip.out","w",stdout);
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        scanf("%s",s[i]+1);
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(s[i][j]=='+'){
                in[i][j]=1;
                out[j][i]=1;
            }
        }
    }
    ll ans=0;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(s[i][j]=='+'){
                t=(in[j])&(out[i]);
                ans+=t.count();
            }
        }
    }
    cout<<ans/3<<endl;
}