Language: Default Desert King Time Limit: 3000MS   Memory Limit: 65536K Total Submissions: 22113   Accepted: 6187 Description David the Great has just become the king of a desert country. To win the respect of his people, he decided to build channels…

                                                                                                Desert King Time Limit: 3000MS   Memory Limit: 65536K Total Submissions: 25729   Accepted: 7143 Description David the Great has just become the king of a…

思路:设sum(cost[i])/sum(dis[i])=r;那么要使r最小,也就是minsum(cost[i]-r*dis[i]);那么就以cost[i]-r*dis[i]为边权重新建边.当求和使得最小生成树的 sum(cost[i]-r*dis[i])==0时,这个r就是最优的.这个证明是01分数规划. #include<iostream> #include<cstdio> #include<cstring> #include<algorithm> #i…

http://poj.org/problem?id=2728 题意: 在这么一个图中求一棵生成树,这棵树的单位长度的花费最小是多少? 思路: 最优比率生成树,也就是01分数规划,二分答案即可,题目很简单,因为这题是稠密图,所以用prim算法会好点. #include<iostream> #include<algorithm> #include<cstring> #include<cstdio> #include<vector> #include&…

/* 迭代法 :204Ms */ #include<stdio.h> #include<string.h> #include<math.h> #define N 1100 #define eps 1e-10 #define inf 0x3fffffff struct node { int u,v,w; }p[N]; double ma[N][N]; double distance(int i,int j) { return sqrt(1.0*(p[i].u-p[j].u…

[题意]每条路径有一个 cost 和 dist,求图中 sigma(cost) / sigma(dist) 最小的生成树. 标准的最优比率生成树,楼教主当年开场随手1YES然后把别人带错方向的题Orz-- ♦01分数规划 参考Amber-胡伯涛神牛的论文<最小割模型在信息学竞赛中的应用> °定义 分数规划(fractional programming)的一般形式: Minimize  λ = f(x) = a(x) / b(x)   ( x∈S  && ∀x∈S, b(x) &…

Desert King http://poj.org/problem?id=2728 Time Limit: 3000MS   Memory Limit: 65536K       Description David the Great has just become the king of a desert country. To win the respect of his people, he decided to build channels all over his country t…

Desert King Time Limit: 3000MS   Memory Limit: 65536K Total Submissions: 20978   Accepted: 5898 [Description] David the Great has just become the king of a desert country. To win the respect of his people, he decided to build channels all over his co…

01分数规划 前置技能 二分思想最短路算法一些数学脑细胞? 问题模型1 基本01分数规划问题 给定nn个二元组(valuei,costi)(valuei,costi),valueivaluei是选择此二元组获得的价值(非负),costicosti是选择此二元组付出的代价(非负),设xi(xi∈{0,1})xi(xi∈{0,1})代表第ii个二元组的选与不选,最大(小)化下式 maximize(or minimize)   r=∑valuei⋅xi∑costi⋅ximaximize(or mini…

题意 n个点完全图,每个边有两个权值,求分数规划要求的东西的最小值. (n<=1000) 题解 心态炸了. 堆优化primT了. 普通的就过了. 我再也不写prim了!!!! 咳咳 最优比率生成树板子题. 公式不是很难推吧. #include<iostream> #include<cmath> #include<iomanip> #include<string.h> ; const int inf=0x7fffffff; using namespace…