POJ 3111 K Best（二分答案）

#include <cstdio>
#include <algorithm>
using namespace std;
const int N=101000;
struct data{int a,b,id;}p[N];
int n,k,ans[N];
double m; 
bool cmp(data a,data b){return a.a-m*a.b>b.a-m*b.b;}
bool check(double x){
    m=x;
    sort(p+1,p+n+1,cmp);
    double tot_v=0,tot_w=0;
    for(int i=1;i<=k;i++){tot_v+=p[i].a;tot_w+=p[i].b;}
    return tot_v/tot_w>x;
}
int main(){
    while(~scanf("%d%d",&n,&k)){
    	double l=0,r=0;
        for(int i=1;i<=n;i++)scanf("%d%d",&p[i].a,&p[i].b),p[i].id=i,r=max(r,(double)p[i].a/p[i].b);
        for(int i=1;i<=100;i++){
            double mid=(l+r)/2;
            if(check(mid))l=mid;
            else r=mid;
        }for(int i=1;i<=k;i++)ans[i]=p[i].id;
		sort(ans+1,ans+k+1); 
		for(int i=1;i<k;i++)printf("%d ",ans[i]);
        printf("%d\n",ans[k]);
    }return 0;
}