https://www.nowcoder.com/acm/contest/143/A

二分答案 转为判定性问题 然后同乘分母后移项 再排序 最后取前(n-k)小是当前最优解 看是都符合条件 复杂度n*logn*logn

#include <bits/stdc++.h>
using namespace std;
#define eps 1e-8

struct node
{
	double s;
	double c;
	double val;
};

node ary[100010];
int n,k;

bool cmp(node n1,node n2)
{
	return n1.s*(n1.c-n1.val)>n2.s*(n2.c-n2.val);
}

bool judge(double val)
{
	double sum;
	int i;
	for(i=1;i<=n;i++) ary[i].val=val;
	sort(ary+1,ary+n+1,cmp);
	sum=0.0;
	for(i=1;i<=n-k;i++)
	{
		sum+=ary[i].s*(ary[i].c-ary[i].val); 
	}
	if(sum<0.0) return false;
	else return true;
}

int main()
{
	double l,r,m,ans;
	int i;
	while(scanf("%d%d",&n,&k)!=EOF)
	{
		for(i=1;i<=n;i++) scanf("%lf",&ary[i].s);
		for(i=1;i<=n;i++) scanf("%lf",&ary[i].c);
		l=0.0,r=1000.0;
		while(r-l>eps)
		{
			m=(l+r)/2.0;
			if(judge(m))
			{
				ans=m;
				l=m;
			}
			else
			{
				r=m;
			}
		}
		printf("%.6f\n",ans);
	}
	return 0;
}