牛客寒假算法基础集训营2 A. 处女座的签到题(数学)

#include <bits/stdc++.h>
#define ll long long
using namespace std;
int n;
struct Node{
	ll x,y;
}a[105];
ll pre[105*105*105];
int k;

int main()
{
	int T;
	scanf("%d",&T);
	while(T--){
		scanf("%d%d",&n,&k);
		for(int i=0;i<n;i++){
			scanf("%lld%lld",&a[i].x, &a[i].y);
		}
		double ans = 0.0;
		int pos = 0;
		for(int i=0;i<n-2;i++){
			for(int j=i+1;j<n-1;j++){
				for(int k=j+1;k<n;k++){
					ll x = a[j].x - a[i].x;
					ll x1 = a[j].y - a[i].y;
					ll y = a[k].x - a[i].x;
					ll y1 = a[k].y - a[i].y;
					ll xx = abs(x * y1 - x1 * y);
					pre[pos++] = xx;
				}
			}
		}
    k = pos - k;
    nth_element(pre, pre + k, pre + pos);
		printf("%lld", pre[k] / 2);
    if(pre[k] % 2 == 1)puts(".50");
    else puts(".00");
	}
	return 0;
}