最短路问题. 从起点和终点开始各跑一次dijkstra,可以得到起点.终点到任意点的距离.枚举使用的商业线路,找最优解. 破题卡输出,记录前驱和输出什么的仿佛比算法本身还麻烦. /*by SilverN*/ #include<algorithm> #include<iostream> #include<cstring> #include<cstdio> #include<cmath> #include<vector> #include…

题目大意:n个点,m条无向边,边权值为正,有k条特殊无向边,起止点和权值已知,求从起点到终点的边权值最小的路径,特殊边最多只能走一条. 题目分析:用两次dijkstra求出起点到任何一个点的最小权值,任何一个点到终点的最小权值,枚举每一条特殊边,取最小的权值. 代码如下: # include<iostream> # include<cstdio> # include<queue> # include<vector> # include<cstring&…

问题描述 洛谷(有翻译) 吐槽 一道坑题. 如何对待商务票 因为商务票只有一张,所以在\(k\)条边中只有一条边会被选中,很显然,最后这条边会被枚举. 如何选择使用商务票的边 假设我们正在枚举这条边,现在的边为\((u,v)\),边权为\(w\). 那么现在的最小代价肯定为 \[min(dist_{(s,u)_{min}}+dist_{(v,e)_{min}}+w,dist_{(s,v)_{min}}+dist_{(u,e)_{min}}+w)\] 其中\(s\)代表起点,\(e\)代表终点,\…

Problem    UVA - 11374 - Airport Express Time Limit: 1000 mSec Problem Description In a small city called Iokh, a train service, Airport-Express, takes residents to the airport more quickly than other transports. There are two types of trains in Airp…

Description Problem D: Airport Express In a small city called Iokh, a train service, Airport-Express, takes residents to the airport more quickly than other transports. There are two types of trains in Airport-Express, the Economy-Xpress and the Comm…

Airport Express Time Limit: 1000ms Memory Limit: 131072KB This problem will be judged on UVA. Original ID: 1137464-bit integer IO format: %lld      Java class name: Main   In a small city called Iokh, a train service, Airport-Express, takes residents…

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=2369 Description Problem D: Airport Express In a small city called Iokh, a train service, Airport-Express, takes residents to the airport more quick…

题意: 在Iokh市中,机场快线是市民从市内去机场的首选交通工具.机场快线分为经济线和商业线两种,线路,速度和价钱都不同.你有一张商业线车票,可以坐一站商业线,而其他时候只能乘坐经济线.假设换乘时间忽略不计,你的任务是找一条去机场最快的路线. 分析: 因为商业线只能走一次,我们就枚举走哪条商业线(或不走),用2次单源最短路分别求从起点和终点出发到所有路的最短路,最后比较即可. 这里我最短路打的是spfa. 代码如下:(注意输出格式) #include<cstdio> #include<c…

In a small city called Iokh, a train service, Airport-Express, takes residents to the airport more quickly than other transports. There are two types of trains in Airport-Express, the Economy-Xpress and the Commercial-Xpress. They travel at different…

最短路. 把题目抽象一下:已知一张图,边上的权值表示长度.现在又有一些边,只能从其中选一条加入原图,使起点->终点的距离最小. 当加上一条边a->b,如果这条边更新了最短路,那么起点st->终点ed的最小距离=st->a  +  a->b  +b->ed 三个值的最短距离之和.于是正反求两次单元最短路.再将k条边遍历一遍就好了. 最近在改代码风格,写起来很别扭..uva又挂了,最让我不理解的是http://www.cnblogs.com/arbitrary/archiv…