最大化平均值

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#include<set>
#include<map>
#include<stack>
#include<bitset>
#include<math.h>
#include<string>
#include<vector>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define pi acos(-1)
#define close ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
using namespace std;
typedef long long ll;
const int MAX_N=1000000+50;
const int INF=0x3f3f3f3f;
ll mod = 1e9+7;

/*
	公式推导
	Σvi/Σwi >= x
	
	Σ(vi - x*wi) >= 0 

*/

int n,k;
int w[MAX_N],v[MAX_N];

double y[MAX_N]; // v - x * w;

//判断是否满足条件
bool C(double x){
	for(int i = 0; i < n; i++){
		y[i] = v[i] - x * w[i];
	}
	sort(y,y+n);
	
	//计算y数组中从大到小前k个数的和
	double sum = 0; 
	for(int i = 0; i < k; i++){
		sum += y[n - i - 1];
	}
	
	return sum >= 0;
} 

void solve(){
	double lb = 0, ub = INF;
	for(int i = 0; i < 100; i++){
		double mid = (lb + ub) / 2;
		if(C(mid)) lb = mid;
		else ub = mid;
	}
	printf("%.2f\n",ub);
}

int main(){
	scanf("%d%d",&n,&k);
	for(int i = 0; i < n; i++){
		scanf("%d%d",&w[i],&v[i]);
	}
	solve();
 	return 0;
}

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*/