Codeforces Round #277.5 (Div. 2), problem: (D) Unbearable Controversy of Being

ㄘ屌屌囉

數一數 a-> ? -> b的個數

include<cstdio>
#include<cstdlib>
#include<cstring>
#include<vector>
#include<map>
using namespace std;
typedef long long int int64;
vector<int> to[3010];
int main()
{
    int n, k; scanf("%d %d", &n, &k);
    for(int lx = 0;lx < k;lx++){
        int a, b;
        scanf("%d %d", &a, &b);
        to[a-1].push_back(b-1);
    }
    int64 count = 0;
    int64 cnt[3010];
    for(int lx = 0;lx < n;lx++){
        //printf("prc on %d\n", lx);
        int qs = 0, qe = 1;
        memset(cnt, 0, sizeof(cnt));
        for(int xx = 0;xx < to[lx].size();xx++){
            int prc = to[lx][xx];
            for(int yy = 0; yy < to[prc].size(); yy++)
                cnt[to[prc][yy]]++;
        }
        for(int xx = 0;xx < n;xx++){
            if(xx == lx) continue;
            //printf("count to %d -> %I64d\n", xx, cnt[xx]);
            count += cnt[xx]*(cnt[xx]-1)/2;
        }
    }
    printf("%I64d\n", count);
//    for(;;);
    return 0;
}