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。
1 #include<iostream> 2 #include<string> 3 #include<algorithm> 4 #include<cstdlib> 5 #include<cstdio> 6 #include<set> 7 #include<map> 8 #include<vector> 9 #include<cstring> 10 #include<stack> 11 #include<cmath> 12 #include<queue> 13 #include <bits/stdc++.h> 14 using namespace std; 15 #define CL(x,v); memset(x,v,sizeof(x)); 16 #define INF 0x3f3f3f3f 17 #define LL long long 18 const int SIGMA_SIZE = 26; 19 const int MAXNODE = 111000; 20 const int MAXS = 150 + 10; 21 const int maxn = 1e5+10; 22 int a[maxn], b[maxn]; 23 int n, p, q; 24 25 double f(double x) 26 { 27 double y = 1; 28 for(int i=0;i<n;i++) y = min(y, (1.0 - x*b[i]) / a[i]); 29 return y*p + x*q; 30 } 31 32 int main() 33 { 34 cin >> n >> p >> q; 35 for(int i=0;i<n;i++) cin >> a[i] >> b[i]; 36 double l=0, r = 1./ (*max_element(b, b+n)); 37 for(int i=0;i<200;i++) 38 { 39 double ll = (l+l+r)/3, rr = (r + r+l)/3; 40 if(f(ll) > f(rr)) r = rr; 41 else l = ll; 42 } 43 printf("%.10f ", f((l+r)*0.5)); 44 return 0; 45 }