解决方案有许多美丽的地方.让我们跳回到到达终点跳回(例如有两点)....无论如何,这不是最短路,但它并不重要.算法能给出正确的结果 思考:而最短的路到同一点例程.spfa先正达恳求一次,求的最短路径的再次的相反,然后列举每个边缘<i,j>查找dist_zheng[i] + len<i,j> + dist_fan[j]的第二小值就可以! 注意不能用邻接矩阵,那样会MLE,应该用邻接表 /* poj 3255 3808K 266MS */ #include<cstdio>…

Roadblocks Time Limit : 4000/2000ms (Java/Other)   Memory Limit : 131072/65536K (Java/Other) Total Submission(s) : 15   Accepted Submission(s) : 6 Problem Description Bessie has moved to a small farm and sometimes enjoys returning to visit one of her…

题目链接 Description Bessie has moved to a small farm and sometimes enjoys returning to visit one of her best friends. She does not want to get to her old home too quickly, because she likes the scenery along the way. She has decided to take the second-s…

题意:给定一个图,求一条1-n的次短路. 析:次短路就是最短路再长一点呗,我们可以和求最短路一样,再多维护一个数组,来记录次短路. 代码如下: #pragma comment(linker, "/STACK:1024000000,1024000000") #include <cstdio> #include <string> #include <cstdlib> #include <cmath> #include <iostream…

Roadblocks Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 12167   Accepted: 4300 Description Bessie has moved to a small farm and sometimes enjoys returning to visit one of her best friends. She does not want to get to her old home too…

Roadblocks http://poj.org/problem?id=3255 Time Limit: 2000MS   Memory Limit: 65536K       Description Bessie has moved to a small farm and sometimes enjoys returning to visit one of her best friends. She does not want to get to her old home too quick…

http://poj.org/problem?id=3255 bessie 有时会去拜访她的朋友,但是她不想走最快回家的那条路,而是想走一条比最短的路长的次短路. 城镇由R条双向路组成,有N个路口.标号为1到N,问1号路口到N号路口的次短路长度是多少?次短路是 比最短路长度长的次短的路径.同一条边可以经过多次. 到某个顶点v的次短路要么帅到其他顶点u的最短路在加上u-v的边,要么是到u的次短路再加上u-v的边, 因此所需要求的就是到所有顶点的最短路和次短路,因此,对于每个顶点,我们记录的不仅仅是…

http://poj.org/problem?id=3255 这道题还是有点难度 要对最短路径的算法非常的了解 明晰 那么做适当的修改 就可以 关键之处 次短的路径: 设u 到 v的边权重为cost 那么到v的次短路径要么是 到u的次短路径+cost:要么是到u的最短路径+cost; 那么就在dijkstra中 既要保存 最短路径的数组 又要 保存次短路径的情况 #include <iostream> #include <stdio.h> #include <string.h…

Roadblocks Time Limit: 2000MS Memory Limit: 65536K Total Submissions: 13216 Accepted: 4660 Description Bessie has moved to a small farm and sometimes enjoys returning to visit one of her best friends. She does not want to get to her old home too quic…

由于次短路一定存在,则可知次短路一定是最短路中某一条边不走,然后回到最短路,而且只是一条边,两条边以上不走的话,就一定不会是次短路了(即以边换边才能使最小).所以可以枚举每一条边,算出从起点到这条边起点的最短距离,以及从终点到这条边终点的最短距离,再加上这条边的权值,看是否是次短路(比最短路总权值大的最小权值的路径) 代码: #include <iostream> #include <cstdio> #include <cstring> #include <cma…