Currency Exchange POJ-1860 这题其实是最短路问题的变形,但是这里不用求解最短路,而是求解路径中是否存在正圈.如果存在正圈则说明兑换后的货币可以一直增加,否则不能实现通过货币转化来增加财富. 这和经典的使用Bellman-Ford判断是否存在负权也有不同的地方,这里需要在松弛方程中,改变判断的条件. package POJ; import java.util.*; public class POJ_1860 { static int n,m,s; static doubl…

---恢复内容开始--- Bellman—Ford算法能在更普遍的情况下(存在负权边)解决单源点最短路径问题.对于给定的带权(有向或无向)图G=(V,E),其源点为s,加权函数w是边集E的映射.对图G运行Bellman—Ford算法的结果是一个布尔值,表明图中是否存在着一个从源点s可达的负权回路.若存在负权回路,单源点最短路径问题无解:若不存在这样的回路,算法将给出从源点s到图G的任意顶点v的最短路径值d[v] Bellman—Ford算法流程 分为三个阶段:       (1)初始化:将除源点…

Bellman - Ford 算法: 一:基本算法 对于单源最短路径问题,上一篇文章中介绍了 Dijkstra 算法,但是由于 Dijkstra 算法局限于解决非负权的最短路径问题,对于带负权的图就力不从心了,而Bellman - Ford算法可以解决这种问题. Bellman - Ford 算法可以处理路径权值为负数时的单源最短路径问题.设想可以从图中找到一个环路且这个环路中所有路径的权值之和为负.那么通过这个环路,环路中任意两点的最短路径就可以无穷小下去.如果不处理这个负环路,程序就会永远运…

链接:poj 1860 题意:给定n中货币.以及它们之间的税率.A货币转化为B货币的公式为 B=(V-Cab)*Rab,当中V为A的货币量, 求货币S通过若干此转换,再转换为原本的货币时是否会添加 分析:这个题就是推断是否存在正权回路.能够用bellman-ford算法,只是松弛条件相反 也能够用SPFA算法,推断经过转换后,转换为原本货币的值是否比原值大... bellman-ford    0MS #include<stdio.h> #include<string.h> str…

Wormholes POJ-3259 这题是最短路问题中判断是否存在负圈的模板题. 判断负圈的一个关键就是理解:如果在图中不存在从s可达的负圈,最短路径不会经过一个顶点两次.while循环最多执行v-1次. 这题还需要注意的是输入的w条边的权值是负值,因为这是虫洞边. package POJ; import java.util.*; public class POJ_3259 { static int f,n,m,w; public int from,to; public double rate…

Currency Exchange 题目链接: http://acm.hust.edu.cn/vjudge/contest/122685#problem/E Description Several currency exchange points are working in our city. Let us suppose that each point specializes in two particular currencies and performs exchange operati…

题意:题目大意:有N个点,给出从a点到b点的距离,当然a和b是互相可以抵达的,问从1到n的最短距离 poj2387 Description Bessie is out in the field and wants to get back to the barn to get as much sleep as possible before Farmer John wakes her for the morning milking. Bessie needs her beauty sleep, s…

Several currency exchange points are working in our city. Let us suppose that each point specializes in two particular currencies and performs exchange operations only with these currencies. There can be several points specializing in the same pair o…

Description Several currency exchange points are working in our city. Let us suppose that each point specializes in two particular currencies and performs exchange operations only with these currencies. There can be several points specializing in the…

Currency Exchange Time Limit: 1000MS   Memory Limit: 30000K Total Submissions: 22123   Accepted: 7990 Description Several currency exchange points are working in our city. Let us suppose that each point specializes in two particular currencies and pe…