WF2017 E

WF最水的题 没有之一 二分答案即可

#include<cstdio> 
#include<cstring>
#include<cmath>
#include<ctime>
#include<iostream>
#include<algorithm>
#include<queue>
#include<set>
#define inf (0x7fffffff)
#define l(a) ((a)<<1)
#define r(a) ((a)<<1|1)
#define b(a) (1<<(a))
#define esp (1e-8)
#define rep(i,a,b) for(int i=a;i<=(b);i++)
#define clr(a) memset(a,0,sizeof(a))
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
int readint(){
    int t=0,f=1;char c=getchar();
    while(!isdigit(c)){
        if(c=='-') f=-1;
        c=getchar();
    }
    while(isdigit(c)){
        t=(t<<3)+(t<<1)+c-'0';
        c=getchar();
    }
    return t*f;
}
const int maxn=10009;
int n,t,a[maxn],b[maxn];
double L=-1e9,R=1e9;
int main(){
    //freopen("#input.txt","r",stdin);
    //freopen("#output.txt","w",stdout);
    n=readint();t=readint();
    rep(i,1,n){
        a[i]=readint();b[i]=readint();
        L=max(L,double(-b[i]+esp));
    }
    while(abs(L-R)>esp){
        double t1=0,mid=(L+R)/2;    //cout<<L<<' '<<R<<' '<<mid<<' ';
        rep(i,1,n) t1+=a[i]*1.0/(b[i]+mid);//cout<<t1<<endl;
        if(t1>t) L=mid;
        else R=mid;
    }
    printf("%.9lf",L);
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}