poj1228

//赚点积分下资源
#include <iostream>#include <algorithm>#include <cmath>using namespace std;#define esp 1e-8struct upoint{double x;double y;}Point[1003];int stack[1003];int N;double Xmult(upoint a,upoint b,upoint c){return (a.x-c.x)*(b.y-c.y)-(b.x-c.x)*(a.y-c.y);}double dis(upoint a,upoint b){return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}bool dayu(double a,double b){return a-esp>b;}bool cmp(upoint a,upoint b){return a.x<b.x||(a.x==b.x&&a.y<b.y);}int tubao(){sort(Point,Point+N,cmp);int top=1;for(int i=0;i<3;i++)stack[i]=i;for(int i=2;i<N;i++){while(top){double x=Xmult(Point[i],Point[stack[top]],Point[stack[top-1]]);double d1=dis(Point[i],Point[stack[top-1]]);double d2=dis(Point[stack[top]],Point[stack[top-1]]);if(x>0)top--;else if(x==0&&dayu(d1,d2))top--;else break;}stack[++top]=i;}int t=top;stack[++top]=N-2;for(int i=N-3;i>=0;i--){while(top>t){double x=Xmult(Point[i],Point[stack[top]],Point[stack[top-1]]);double d1=dis(Point[i],Point[stack[top-1]]);double d2=dis(Point[stack[top]],Point[stack[top-1]]);if(x>0)top--;else if(x==0&&dayu(d1,d2))top--;else break;}stack[++top]=i;}return top;}bool manzu(int i,int j,int k){return 0==(Point[i].x-Point[k].x)*(Point[j].y-Point[k].y)-(Point[i].y-Point[k].y)*(Point[j].x-Point[k].x);}bool nothave(int i,int j){for(int k=0;k<N;k++)if(k!=i&&k!=j){if(manzu(i,j,k))return false;}return true;}int main(){int kase;cin>>kase;while(kase--){cin>>N;for(int i=0;i<N;i++){int a,b;cin>>a>>b;Point[i].x=1.0*a;Point[i].y=1.0*b;}if(N<=5){cout<<"NO\n";continue;}int top=tubao();if(top<3){cout<<"NO\n";continue;}int yes=1;for(int i=1;i<top;i++){int j=i-1;if(nothave(stack[i],stack[j])){yes=0;break;}}if(nothave(stack[top-1],stack[0]))yes=0;if(yes)cout<<"YES\n";else cout<<"NO\n";}return 0;}
//0 1 0 2 0 3 0 4 0 5 NO
//N<=5 NO
//TOP<3 NO~