Til the Cows Come Home POJ - 2387
来源:互联网 发布:linux top 所有进程 编辑:程序博客网 时间:2024/06/04 23:31
Description
Bessie is out in the field and wants to get back to the barn to get as much sleep as possible before Farmer John wakes her for the morning milking. Bessie needs her beauty sleep, so she wants to get back as quickly as possible.
Farmer John’s field has N (2 <= N <= 1000) landmarks in it, uniquely numbered 1..N. Landmark 1 is the barn; the apple tree grove in which Bessie stands all day is landmark N. Cows travel in the field using T (1 <= T <= 2000) bidirectional cow-trails of various lengths between the landmarks. Bessie is not confident of her navigation ability, so she always stays on a trail from its start to its end once she starts it.
Given the trails between the landmarks, determine the minimum distance Bessie must walk to get back to the barn. It is guaranteed that some such route exists.
Input
* Line 1: Two integers: T and N
- Lines 2..T+1: Each line describes a trail as three space-separated integers. The first two integers are the landmarks between which the trail travels. The third integer is the length of the trail, range 1..100.
Output - Line 1: A single integer, the minimum distance that Bessie must travel to get from landmark N to landmark 1.
Sample Input
5 5
1 2 20
2 3 30
3 4 20
4 5 20
1 5 100
Sample Output
90
Hint
INPUT DETAILS:
There are five landmarks.
OUTPUT DETAILS:
Bessie can get home by following trails 4, 3, 2, and 1.
问题概述
第一行输入T,N接下来的T行输入点v,u以及边长v,u的权重。N代表有1~N个点。
求母牛从N走到1的最短路径。
问题分析
采用Dijstra算法,注意输入的数据中可能会有相同的边,要取权重最小的一条。
Dijstra算法描述。
集合S起始值为始发顶点N(作为新加入的顶点)
集合u起始值为除N以外的其他顶点。
1.遍历新加入到S中节点的孩子节点(只在u不在s中)跟新它们到起始顶点N的距离(一开始为正无穷)
2.将u中到达N距离最短的顶点加入到s中
3.重复步骤1与2直到u为空。
注:s中顶点存储的值为该顶点到达N的最小值
知识点介绍
truct cmp{ bool operator()(int x,int y){ return result[x]>result[y]; }};priority_queue<int,vector<int>,cmp> que;
自定义优先队列<比较。
代码实现
#include<iostream>#include<cstdio>#include<queue>#include<vector>using namespace std;#define INF 1<<29#define maxi 1002int map[maxi][maxi];int result[maxi];int s[maxi];vector<int>vec[maxi];struct cmp{ bool operator()(int x,int y){ return result[x]>result[y]; }};priority_queue<int,vector<int>,cmp> que;int dfs(int N){ int vis[maxi]={0}; vis[N]=1; while(!que.empty()){ int temp=que.top(); que.pop(); if(temp==1)return result[temp]; s[temp]=1; for(int i=1;i<N+1;i++) if(map[temp][i]!=INF&&s[i]==0){ if(map[temp][i]+result[temp]<result[i]) result[i]=map[temp][i]+result[temp]; if(vis[i]==0)que.push(i); vis[i]=1; } }}int main(){ int T,N; scanf("%d %d",&T,&N); for(int i=1;i<N+1;i++){ result[i]=INF; s[i]=0; for(int j=1;j<N+1;j++) map[i][j]=INF; } for(int i=1;i<T+1;i++){ int v1,v2,w; scanf("%d %d %d",&v1,&v2,&w); if(map[v1][v2]>w)map[v2][v1]=map[v1][v2]=w; } que.push(N); result[N]=0; printf("%d\n",dfs(N)); return 0;}
- POJ 2387 Til the Cows Come Home
- poj 2387 Til the Cows Come Home
- poj 2387 Til the Cows Come Home
- poj 2387 Til the Cows Come Home
- POJ 2387 Til the Cows Come Home
- POJ 2387 Til the Cows Come Home
- POJ 2387 Til the Cows Come Home
- Poj 2387 Til the Cows Come Home
- poj 2387 Til the Cows Come Home
- POJ 2387 Til the Cows Come Home
- poj 2387 Til the Cows Come Home
- POJ-2387-Til the Cows Come Home
- poj 2387 Til the Cows Come Home
- poj 2387 Til the Cows Come Home
- POJ 2387 Til the Cows Come Home
- POJ 2387 Til the Cows Come Home
- POJ 2387 Til the Cows Come Home
- POJ 2387 Til the Cows Come Home
- 浅析muduo库中的线程设施02
- mysql中replace into的用法
- RDTSC
- 2.19.5 奇数乘积
- 我喜欢这里的气氛
- Til the Cows Come Home POJ - 2387
- 大数据技术
- pyc5
- Java获取IP地址的多种方法
- 解决Ubuntu和Windows的文件乱码问题
- cs231n的第一次作业2层神经网络
- Android Service使用详解
- mysql编码设置为utf8
- SWIG学习入门(一)