题目大意:给出n个点,m条无向边,每条边有长度.求一棵树,要求树上的每个点到源点距离最小的前提下,使得树上的边的长度和最小.输出树上边的总长度,以及树上的边的序号(按输入顺序 1...m). 思路 :单源最短路径 + 贪心 .用Dijkstra 或spfa 算法 求每个点到源点的最短路径,并在记录当前用来更新每个点最短距离的那条边(即pre[i]记录点i所对应的变).  若当前这条边能使得某个点到源点的距离变小则更新该点到源点的距离,并记录更新该点的边; 若当前这条边更新某节点后,使得该点到源点…

E. Paths and Trees time limit per test: 3 seconds memory limit per test: 256 megabytes input: standard input output: standard output Little girl Susie accidentally found her elder brother's notebook. She has many things to do, more important than sol…

题目链接 题意:给定一个无向图和一个点u,找出若干条边组成一个子图,要求这个子图中u到其他个点的最短距离与在原图中的相等,并且要求子图所有边的权重之和最小,求出最小值并输出子图的边号. 思路:先求一遍最短路,从所有到i点的满足最短路的边中选一条权最小的边. Java程序 import java.io.PrintStream; import java.util.ArrayList; import java.util.LinkedList; import java.util.List; import…

[题目大意] 题目将从某点出发的所有最短路方案中,选择边权和最小的最短路方案,称为最短生成树. 题目要求一颗最短生成树,输出总边权和与选取边的编号.[题意分析] 比如下面的数据: 5 5 1 2 2 2 3 2 3 4 16 1 5 18 4 5 2 1 这个图对于从 1 出发,有两种最短路. 这种最短路方案中 dis[2]=2,dis[3]=4,dis[4]=20,dis[5]=18.边权总和 Sum=44 但如果这样选边,1点到各点的距离依然为最短路,但Sum降为了24. 那么如何选择到最优…

[题目链接] https://codeforces.com/contest/545/problem/E [算法] 首先求 u 到所有结点的最短路 记录每个节点最短路径上的最后一条边         答案即为以u为根的一棵最短路径生成树 时间复杂度 : O(NlogN) [代码] #include<bits/stdc++.h> using namespace std; ; const long long INF = 1e60; struct edge { int to , w , nxt; }…

E. Paths and Trees time limit per test:3 seconds memory limit per test:256 megabytes input:standard input output:standard output Little girl Susie accidentally found her elder brother's notebook. She has many things to do, more important than solving…

题目链接: 题目 E. Paths and Trees time limit per test 3 seconds memory limit per test 256 megabytes inputstandard input outputstandard output 问题描述 Little girl Susie accidentally found her elder brother's notebook. She has many things to do, more important…

E. Paths and Trees time limit per test 3 seconds memory limit per test 256 megabytes input standard input output standard output Little girl Susie accidentally found her elder brother's notebook. She has many things to do, more important than solving…

E. Paths and Trees time limit per test 3 seconds memory limit per test 256 megabytes input standard input output standard output Little girl Susie accidentally found her elder brother's notebook. She has many things to do, more important than solving…

Paths and Trees time limit per test3 seconds memory limit per test256 megabytes Little girl Susie accidentally found her elder brother's notebook. She has many things to do, more important than solving problems, but she found this problem too interes…