BZOJ 2916 Monochromatic Triangles

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<bitset>
#define maxn 1005
using namespace std;
int n,m,ans=0,x,y;
bitset <maxn> map[maxn],regis;
int main()
{
    scanf("%d%d",&n,&m);
    for (int i=1;i<=m;i++)
    {
        scanf("%d%d",&x,&y);
        map[x][y]=1;map[y][x]=1;
    }    
    for (int i=1;i<=n;i++)
        for (int j=i+1;j<=n;j++)
        {
            if (!map[i][j]) continue;
            regis=map[i]&map[j];
            ans+=regis.count();    
        }
    for (int i=1;i<=n;i++)
        for (int j=1;j<=n;j++)
        {
            if (i==j) continue;
            map[i][j]=map[i][j]^1;
        }
    for (int i=1;i<=n;i++)
        for (int j=i+1;j<=n;j++)
        {
            if (!map[i][j]) continue;
            regis=map[i]&map[j];
            ans+=regis.count();    
        }
    printf("%d\n",ans/3);
    return 0;
}