codeforce 605BE. Freelancer's Dreams

题意：给你n个工程，做了每个工程相应增长x经验和y钱。问你最少需要多少天到达制定目标。时间可以是浮点数。

思路：杜教思路，用对偶原理很简易。个人建议还是标准解题法，凸包+线性组合。

#include<iostream>
#include<string>
#include<algorithm>
#include<cstdlib>
#include<cstdio>
#include<set>
#include<map>
#include<vector>
#include<cstring>
#include<stack>
#include<cmath>
#include<queue>
#include <bits/stdc++.h>
using namespace std;
#define CL(x,v); memset(x,v,sizeof(x));
#define INF 0x3f3f3f3f
#define LL long long
const int SIGMA_SIZE = 26;
const int MAXNODE = 111000;
const int MAXS = 150 + 10;
const int maxn = 1e5+10;
int a[maxn], b[maxn];
int n, p, q;

double f(double x)
{
    double y = 1;
    for(int i=0;i<n;i++) y = min(y, (1.0 - x*b[i]) / a[i]);
    return y*p + x*q;
}

int main()
{
    cin >> n >> p >> q;
    for(int i=0;i<n;i++) cin >> a[i] >> b[i];
    double l=0, r = 1./ (*max_element(b, b+n));
    for(int i=0;i<200;i++)
    {
        double ll = (l+l+r)/3, rr = (r + r+l)/3;
        if(f(ll) > f(rr)) r = rr;
        else l = ll;
    }
    printf("%.10f
", f((l+r)*0.5));
    return 0;
}