961D - Pair Of Lines - CodeForces Solution

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int read()
{
	int x;scanf("%d",&x);return x;
}
int n;
ll x[100010],y[100010];
void work(int X1,int X2)
{
	int X3=0,X4=0;
	for(int i=1;i<=n;i++)
	{
		if(i==X1||i==X2)
			continue;
		if(X3&&X4)
		{
			if((y[i]-y[X2])*(x[X2]-x[X1])!=(y[X2]-y[X1])*(x[i]-x[X2])&&(y[i]-y[X4])*(x[X4]-x[X3])!=(y[X4]-y[X3])*(x[i]-x[X4]))
				return ;
		}
		else if((y[i]-y[X2])*(x[X2]-x[X1])!=(y[X2]-y[X1])*(x[i]-x[X2]))
		{
			if(X3)
				X4=i;
			else
				X3=i;
		}
	}
	printf("YES");
	exit(0);
}
int main()
{
	// freopen("1.in","r",stdin);
	n=read();
	for(int i=1;i<=n;i++)
		x[i]=read(),y[i]=read();
	work(1,2);
	work(2,3);
	work(1,3);
	printf("NO");
}