由题意可知,我们需要求的是很多个点到同一个店的最短距离,然后再求同一个点到很多个点的最短距离. 对于后者我们很好解决,就是很经典的单源最短路径,跑一边dijkstra或者SPFA即可. 然而对于前者,我们应该怎么解决呢?难道我们需要求一边Floyd?当然不可能!\(O(n^3)\)的时间复杂度,对于我们的\(n<=1000\)是果断要超时的. 深入分析,对于一张图,A到B的最短距离,应该等于B到A,在反转一张图以后的最短距离.所谓反转一张图,就是把变得方向调转.这一点是很显然的! 因此,对于问题…

P1821 [USACO07FEB]银牛派对Silver Cow Party 题目描述 One cow from each of N farms (1 ≤ N ≤ 1000) conveniently numbered 1..N is going to attend the big cow party to be held at farm #X (1 ≤ X ≤ N). A total of M (1 ≤ M ≤ 100,000) unidirectional (one-way roads co…

P1821 [USACO07FEB]银牛派对Silver Cow Party 题目描述 One cow from each of N farms (1 ≤ N ≤ 1000) conveniently numbered 1..N is going to attend the big cow party to be held at farm #X (1 ≤ X ≤ N). A total of M (1 ≤ M ≤ 100,000) unidirectional (one-way roads co…

题目描述 One cow from each of N farms (1 ≤ N ≤ 1000) conveniently numbered 1..N is going to attend the big cow party to be held at farm #X (1 ≤ X ≤ N). A total of M (1 ≤ M ≤ 100,000) unidirectional (one-way roads connects pairs of farms; road i requires…

题目描述 One cow from each of N farms (1 ≤ N ≤ 1000) conveniently numbered 1..N is going to attend the big cow party to be held at farm #X (1 ≤ X ≤ N). A total of M (1 ≤ M ≤ 100,000) unidirectional (one-way roads connects pairs of farms; road i requires…

题目描述 One cow from each of N farms (1 ≤ N ≤ 1000) conveniently numbered 1..N is going to attend the big cow party to be held at farm #X (1 ≤ X ≤ N). A total of M (1 ≤ M ≤ 100,000) unidirectional (one-way roads connects pairs of farms; road i requires…

更好的阅读体验 Portal Portal1: Luogu Portal2: POJ Description One cow from each of N farms \((1 \le N \le 1000)\) conveniently numbered \(1 \cdots N\) is going to attend the big cow party to be held at farm #X \((1 \le X \le N)\). A total of \(M (1 \le M \l…

题目简叙: 寒假到了,N头牛都要去参加一场在编号为X(1≤X≤N)的牛的农场举行的派对(1≤N≤1000),农场之间有M(1≤M≤100000)条有向路,每条路长Ti(1≤Ti≤100). 每头牛参加完派对后都必须回家,无论是去参加派对还是回家,每头牛都会选择最短路径,求这N头牛的最短路径(一个来回)中最长的一条路径长度. 分析: 其实这道题的考点就是单元最短路径和单终点最短路径. 单终点最短路径其实就可以把所有的边反过来,直接就转换为单源最短路径了. 于是此题的核心就是跑两遍dijkstra或…

银牛排队 对于我这种蒟蒻来说,还是不要跑一次单元最短路.跑两次好写呀(-￣▽￣)- 而题目中是有向图.如果如果按照题意进行最短路的话.就会出现一个单终点最短路和一个单起点最短路 对于单起点自然就是套模板,但对于单终点最短路怎么办呢? 显而易见的是,只有一个终点废话呢你(/ﾟДﾟ)/ 这样我们就可以反向存一次有向边.将终点变为起点,这样的话就可以套模板了合着就是刷模板题呀(▼⊿▼) #include<iostream> #include<cstdio> #include<que…

银牛派对 正向建图+反向建图, 两边跑dijkstra,然后将结果相加即可. 反向建图以及双向建图的做法是学习图论的必备思想. #include <iostream> #include <cstdio> #include <cstring> #include <queue> using namespace std; //Mystery_Sky // #define maxn 1000010 #define maxm 5000050 #define INF 0…