CodeForces - 13D Triangles

#include<iostream>
#include<cstring>
#include<cmath>
#include<assert.h>
#include<stdio.h>
using namespace std;

typedef __int64 lld;
const int INF=1000000000;
struct P
{
lld x,y;
P(){};
P(lld x,lld y):x(x),y(y){};
P operator -(const P & b)const
{
P tmp(x-b.x,y-b.y);
return tmp;
}
};

lld cross(P a,P b)
{
return a.x*b.y-a.y*b.x;
}

P red[505],blue[505];
int cnt[505][505];
int main()
{
int i,j,k;
int N,M;
lld x,y;
memset(cnt,0,sizeof(cnt));
freopen("D:\\codeforces\\D. Triangles\\data\\20.in","r",stdin);
freopen("D:\\codeforces\\D. Triangles\\data\\20.out","w",stdout);
cin>>N>>M;
assert(N>=0&&N<=500);
assert(M>=0&&M<=500);
for(i=0;i<N;i++)
{
cin>>x>>y;
assert(x>=-INF&&x<=INF);
assert(y>=-INF&&y<=INF);
red[i]=P(x,y);
}
for(i=0;i<M;i++)
{
cin>>x>>y;
assert(x>=-INF&&x<=INF);
assert(y>=-INF&&y<=INF);
blue[i]=P(x,y);
}

for(i=0;i<N;i++)
{
for(j=0;j<N;j++)
{
if(i==j||red[i].x>red[j].x)continue;
for(k=0;k<M;k++)
{
if(blue[k].x>=red[i].x&&blue[k].x<red[j].x&&cross(blue[k]-red[i],red[j]-red[i])>0)
cnt[i][j]++;
}
cnt[j][i]=-cnt[i][j];
}
}

int ans=0;
for(i=0;i<N;i++)
{
for(j=i+1;j<N;j++)
for(k=j+1;k<N;k++)
{
if(cnt[i][j]+cnt[j][k]+cnt[k][i]==0)
ans++;
}
}
cout<<ans<<endl;
return 0;
}