思路: 这题就是判断存不存在负环回路。 前M条是双向边,后面的W是单向的负边。 为了防止出现不连通,增加一个结点作为起点。起点到所有点的长度为0 #include <iostream> #include <stdio.h> #include <string.h> #include <algorithm> #include <vector> using namespace std; /* * 单源最短路bellman_ford...
Bellman - ford算法是求含负权图的单源最短路径算法,效率很低,但代码很容易写。其原理为持续地进行松弛(原文是这么写的,为什么要叫松弛,争议很大),在每次松弛时把每条边都更新一下,若在n-1次松弛后还能更新,则说明图中有负环,因此无法得出结果,否则就完成。Bellman - ford算法有一个小优化:每次松弛先设一个...
While exploring his many farms, Farmer John has discovered a number of amazing wormholes. A wormhole is very peculiar because it is a one-way path that delivers you to its destination at a time that is BEFORE you entered the wormhole! Each of FJ’s farms comprises N (1 ≤ N ≤ 500) ...
POJ3259 Wormholes —— spfa求负环 Wormholes Description While exploring his many farms, Farmer John has discovered a number of amazing wormholes. A wormhole is very peculiar because it is a one-way path that delivers you to its destination at a time that is BEFORE you entered the wormhole!
Wormholes—POJ3259 简介:Wormholes—POJ3259 Problem Description While exploring his many farms, Farmer John has discovered a number of amazing wormholes. A wormhole is very peculiar because it is a one-way path that delivers you to its destination at a time that is BEFORE you entered the ...
poj3259 Wormholes 农夫约翰在探索他的许多农场,发现了一些惊人的虫洞。虫洞是很奇特的,因为它是一个单向通道,可让你进入虫洞的前达到目的地!他的N(1≤N≤500)个农场被编号为1..N,之间有M(1≤M≤2500)条路径,W(1≤W≤200)个虫洞。FJ作为一个狂热的时间旅行的爱好者,他要做到以下几点:开始在一个区域,...
poj3259 - Wormholes (bellman_ford/spfa求负环模板题) 2018-12-04 17:54 − 题目链接:http://poj.org/problem?id=3259 题意:一个农场主,有n个农场,农场之间有m条双向路,每条路有花费时间权值,有w个虫洞以路的形式给出,权值为可以回到多久之前。 思路:虫洞可以看成是一条负权路,问题就转化成求一个...
POJ3259-Wormholes //SPFA或Bellman Ford算法 //判断是否有负权值回路 //Time:172Ms Memory:252K #include<iostream> #include<cstring> #include<cstdio> #include<queue> using namespace std; #define MAX 505 #define MAXN 5500 #define INF 0x3f3f3f3f struct Edge { int u, w, next; Edge() {...
POJ 3259(Wormholes) 链接:https://vjudge.net/problem/POJ-3259 思路:一个裸着的判断是否存在负环即可,可用Bellman-Ford算法判断负环的形式,但是一定要注意,秘密通道和走廊是可以同时存在,也就是既要花费时间也要回溯时间。 代码: #include<iostream>#include<cstring>usingnamespacestd;structedge{intfrom,to,...
POJ 3259 Wormholes(spfa判负环) 题目链接:http://poj.org/problem?id=3259 题意是有n个点,m条边,k个虫洞(权值为负),输入完m条无向边后输入k条有向边,问能不能找到一个点,从这个点出发,最后回到这个点的时候权值是负的(时光倒流)。 首先这个可以用Floyd去跑一遍,然后遍历每个点看看有没有能得到...