zoukankan      html  css  js  c++  java
  • [POJ1847] Tram

    Description

    Tram network in Zagreb consists of a number of intersections and rails connecting some of them. In every intersection there is a switch pointing to the one of the rails going out of the intersection. When the tram enters the intersection it can leave only in the direction the switch is pointing. If the driver wants to go some other way, he/she has to manually change the switch.

    When a driver has do drive from intersection A to the intersection B he/she tries to choose the route that will minimize the number of times he/she will have to change the switches manually.

    Write a program that will calculate the minimal number of switch changes necessary to travel from intersection A to intersection B.

    Input

    The first line of the input contains integers N, A and B, separated by a single blank character, 2 <= N <= 100, 1 <= A, B <= N, N is the number of intersections in the network, and intersections are numbered from 1 to N.

    Each of the following N lines contain a sequence of integers separated by a single blank character. First number in the i-th line, Ki (0 <= Ki <= N-1), represents the number of rails going out of the i-th intersection. Next Ki numbers represents the intersections directly connected to the i-th intersection.Switch in the i-th intersection is initially pointing in the direction of the first intersection listed.

    Output

    The first and only line of the output should contain the target minimal number. If there is no route from A to B the line should contain the integer "-1".

    Sample Input

    3 2 1
    2 2 3
    2 3 1
    2 1 2
    

    Sample Output

    0
    

    Source

    Croatia OI 2002 Regional - Juniors

    题解

    关键在于读懂题目,再就是简单的(Dijkstra)

    #include<iostream>
    #include<cstdio>
    #include<cstdlib>
    #include<queue>
    #include<cstring>
    #include<string>
    #include<algorithm>
    #include<cstdlib>
    #include<cmath>
    #include<map>
    #include<vector>
    #include<set>
    #include<bitset>
    #include<stack>
    using namespace std;
    
    const int N=101,NE=10001;
    int n,From,End;
    struct edge
    {
    	int v,w,nx;
    }e[NE];
    int ne,hd[N];
    
    void Build(int u,int v,int w)
    {
    	++ne,e[ne]=(edge){v,w,hd[u]},hd[u]=ne;
    }
    
    void Read()
    {
    	scanf("%d%d%d",&n,&From,&End);
    	int num,to;
    	for(int i=1;i<=n;++i)
    	{
    		scanf("%d",&num);
    		for(int j=0;j<num;++j)
    		{
    			scanf("%d",&to);
    			if(j) Build(i,to,1);
    			else Build(i,to,0);
    		}
    	}
    }
    
    typedef pair<int,int> pr;
    priority_queue<pr,vector<pr>,greater<pr> >Q;
    bool vis[N];
    int dis[N];
    const int INF=10000000;
    
    void Dijkstra(int s)
    {
    	for(int i=1;i<=n;++i) dis[i]=INF;
    	dis[s]=0;
    	Q.push(make_pair(dis[s],s));
    	int nw,to,YH;
    	while(!Q.empty())
    	{
    		nw=Q.top().second;
    		Q.pop();
    		if(vis[nw]) continue;
    		vis[nw]=1;
    		for(int i=hd[nw];i;i=e[i].nx)
    		{
    			to=e[i].v,YH=dis[nw]+e[i].w;
    			if(dis[to]>YH)
    			{
    				dis[to]=YH;
    				Q.push(make_pair(dis[to],to));
    			}
    		}
    	}
    }
    
    int main()
    {
    	Read(),Dijkstra(From);
    	if(dis[End]<INF) printf("%d
    ",dis[End]);
    	else puts("-1");
    	return 0;
    }
    

    本文作者:OItby @ https://www.cnblogs.com/hihocoder/

    未经允许,请勿转载。

  • 相关阅读:
    Java快速教程
    让我们来了解一下:操作系统和平台相关性
    初窥Linux 之 我最常用的20条命令
    ES6学习笔记一
    Data时间管理大全
    generator多返回值写法
    箭头函数=>
    闭包
    高阶函数:map/reduce
    函数方法that与apply
  • 原文地址:https://www.cnblogs.com/hihocoder/p/11479822.html
Copyright © 2011-2022 走看看