codeforces 682 E. Alyona and Triangles（三角形，对称）

题目链接 codeforces 682E

题意

   给出n个点，任意三个点组成的三角形面积等于S ，找到一个三角形包含全部点，且面积小于4S

 先找出最大三角形的三个点，然后A做关于BC中点对称，B做关于AC中点对称，C做关于AB中点对称。

 

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
typedef long long ll;
ll n;
ll x[5005],y[5005];
ll getArea(ll a,ll b,ll c){
   return abs((x[b]-x[a])*(y[c]-y[a])-(x[c]-x[a])*(y[b]-y[a]));
}
int main(){
   ll i,j,k,s;
   scanf("%lld%lld",&n,&s);
   for(i = 1; i <= n; i++){
	scanf("%lld%lld", &x[i], &y[i]);
    }
    ll a = 1,b = 2, c = 3;
    while(1){
	ll flag = 0;
	for(i = 1; i <= n; i++){
		s = getArea(a,b,c);
		if(s < getArea(i,b,c))a = i,flag = 1;
		else if(s<getArea(a,i,c))b = i,flag = 1;
		else if(s<getArea(a,b,i))c = i,flag = 1;
	}
	if(!flag)break;
    }
   cout<< (x[a]+x[b]-x[c]) << " " << (y[a]+y[b]-y[c]) <<endl;
   cout<< (x[a]+x[c]-x[b]) << " " << (y[a]+y[c]-y[b]) <<endl;
   cout<< (x[b]+x[c]-x[a]) << " " << (y[b]+y[c]-y[a]) <<endl;
   return 0; 
}