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 = ;
 const int MAXNODE = ;
 const int MAXS =  + ;
 const int maxn = 1e5+;
 int a[maxn], b[maxn];
 int n, p, q;

 double f(double x)
 {
     double y = ;
     for(int i=;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=;i<n;i++) cin >> a[i] >> b[i];
     double l=, r = ./ (*max_element(b, b+n));
     for(int i=;i<;i++)
     {
         double ll = (l+l+r)/, rr = (r + r+l)/;
         if(f(ll) > f(rr)) r = rr;
         else l = ll;
     }
     printf("%.10f\n", f((l+r)*0.5));
     return ;
 }