# hihoCoder#1879 : Rikka with Triangles (计算几何)

n<=2000，肯定没有办法把所有三角形找出来全判一遍

#include <bits/stdc++.h>
#define ll long long
#define big __int128
#define eps 1e-8
#define mod 998244353
using namespace std;
const int maxn = 2005;
int sgn(double x)
{
if (fabs(x) < eps)
return 0;
if (x < 0)
return -1;
return 1;
}
struct Point
{
big x, y;
Point() {}
Point(big _x, big _y)
{
x = _x;
y = _y;
}
Point operator+(const Point &b) const
{
return Point(x + b.x, y + b.y);
}
Point operator-(const Point &b) const
{
return Point(x - b.x, y - b.y);
}
big operator*(const Point &b) const
{
return x * b.x + y * b.y;
}
big operator^(const Point &b) const
{
return x * b.y - y * b.x;
}
void Mod()
{
bool tx = false, ty = false;
if (x < 0)
{
x = -x;
tx = true;
}
if (y < 0)
{
y = -y;
ty = true;
}
x %= mod;
y %= mod;
if (tx)
x = -x;
if (ty)
y = -y;
}
int getxx()
{
if (x > 0 && y >= 0)
return 1;
if (x <= 0 && y > 0)
return 2;
if (x < 0 && y <= 0)
return 3;
if (x >= 0 && y < 0)
return 4;
return 5;
}
} a[maxn],del[maxn];
bool cmp(Point &a,Point &b){
if(a.getxx() != b.getxx()){
return a.getxx() < b.getxx();
}else{
return (a^b)>0;
}
}
int n;
big ans;
void gao(int id){
Point now = a[id];
int m = 0;
for(int i = 1;i <= n;i++){
if(i==id)continue;
del[++m] = a[i]-now;
//del[m].Mod();
}
if(m<=1)return;
sort(del+1,del+1+m,cmp);
int p1 = 1,p2 = 1;
Point s1=del[1],s2=del[1],ts1,ts2;
for(int i = 1;i <= m;i++){
int nxt;
while(true){
nxt = p1+1;
if(nxt>m)nxt=1;
if(nxt==i)break;
if(!((del[i]^del[nxt])>=0&&(del[i]*del[nxt])>0))break;
if((del[i]^del[nxt])==0&&(del[i]^del[p1])!=0)break;
p1=nxt;s1=s1+del[p1];
}
while(true){
nxt = p2+1;
if(nxt>m)nxt=1;
if(nxt==i)break;
if(!((del[i]^del[nxt])>=0))break;
if((del[i]^del[nxt])==0&&(del[i]^del[p2])!=0)break;
p2=nxt;s2=s2+del[p2];
}
ts1=s1;ts2=s2-s1;ts1.Mod();ts2.Mod();
ans+=(del[i]^ts1);ans %= mod;
ans-=(del[i]^ts2)%mod*2ll%mod;
ans=(ans+mod)%mod;
if(p1==i){p1++;s1=s1+del[p1];}s1=s1-del[i];
if(p2==i){p2++;s2=s2+del[p2];}s2=s2-del[i];
}

}
int main()
{
int T;
scanf("%d",&T);
big inv = (mod+1)/3;
while (T--)
{
scanf("%d",&n);
ans=0;
for (int i = 1; i <= n; i++)
{
ll x, y;
scanf("%lld%lld",&x,&y);
a[i] = Point(x, y);
}

for(int i= 1;i <= n;i++){
gao(i);
}
ans=(ans*inv)%mod;
ll t = ans;
printf("%lld\n",t);
}
return 0;
}

posted @ 2019-10-21 11:45  ACforever  阅读(364)  评论(0编辑  收藏  举报