地铁最短路径需求分析

 

 

功能需求：

提供一副地铁线路图，计算指定两站之间最短（最少经过站数）乘车路线；输出指定地铁线路的所有站点。

 

以北京地铁为例，地铁线路信息保存在data.txt中，格式如下：

地铁线路总数

线路名1 站名1 站名2 站名3 ...

线路名2 站名1 站名2 站名3 ...

线路名3 站名1 站名2 站名3 ......

实现语言：java

主要功能：读取地铁线，算最短路径

需求分析：能在短时间内为用户提供路线

主要算法：SPFA算法

类职责划分：public static void SPFA(int s)算最短路

public static void ReadIn(String Path)读取文件

将来需求：提供路线的相应费用

数据需求：顺利读出txt文件提供数据

github链接：https://github.com/ytl31801299/subwayroute

测试截图：

 

 

 

 代码部分：

import java.io.*;
import java.util.*;

public class Main
{
    public static ArrayList<ArrayList<Integer>> g;
    public static HashMap<String, Integer> norm;
    public static HashMap<Integer, String> unnorm;
    public static int cnt;
    public static void ReadIn(String Path)
    {
        cnt = 0;
        g = new ArrayList<ArrayList<Integer>>();
        norm = new HashMap<String, Integer>();
        unnorm = new HashMap<Integer, String>();
        File f = new File(Path);
        if(!f.exists() || !f.isFile())
        {
            System.out.println("Error reading file");
            System.exit(1);
        }
        try
        {
            FileInputStream fileInputStream = new FileInputStream(f);
            InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream, "UTF-8");
            BufferedReader reader = new BufferedReader(inputStreamReader);
            String lineContent = "";
            while ((lineContent = reader.readLine()) != null)
            {
                String[] gates = lineContent.split(" ");
                if(gates.length <= 1)continue;
                int last = -1;
                for(int i = 1; i < gates.length;i++)
                {
                    String x = gates[i];
                    if(!norm.containsKey(x))
                    {
                        norm.put(x, cnt);
                        unnorm.put(cnt, x);
                        ++cnt;
                        g.add(new ArrayList<Integer>());
                    }
                    if(last != -1)
                    {
                        g.get(last).add(norm.get(x));
                        g.get(norm.get(x)).add(last);
                    }
                    last = norm.get(x);
                }
            }
            fileInputStream.close();
            inputStreamReader.close();
            reader.close();
            return;
        }
        catch(Exception e)
        {
            e.printStackTrace();
            System.exit(1);
        }
    }
    public static int[] dist;
    public static int[] upd;
    public static boolean[] inqueue;
    public static final int INF = 0x23333333;//infinity
    public static void SPFA(int s)
    {
        for(int i=0;i<cnt;i++)
        {
            dist[i] = INF;
            upd[i] = -1;
            inqueue[i] = false;
        }
        dist[s] = 0;
        Queue<Integer> q = new LinkedList<Integer>();
        q.offer(s);
        while(!q.isEmpty())
        {
            int f = q.poll();
            for(int x: g.get(f))
            {
                if(dist[x] > dist[f] + 1)
                {
                    dist[x] = dist[f] + 1;
                    upd[x] = f;
                    if(!inqueue[x])
                    {
                        inqueue[x] = true;
                        q.offer(x);
                    }
                }
            }
        }
    }
    public static void main(String[] args)
    {
        ReadIn("data.txt");
        dist = new int[cnt];
        upd = new int[cnt];
        inqueue = new boolean[cnt];
        Scanner sc = new Scanner(System.in);
        while(true)
        {
            System.out.print("请输入起点站: ");
            String frm = sc.next();
            if(!norm.containsKey(frm))
            {
                System.out.println("您输入的起点站不是一个地铁站");
                continue;
            }
            System.out.print("请输入终点站: ");
            String dest = sc.next();
            if(!norm.containsKey(dest))
            {
                System.out.println("您输入的终点站不是一个地铁站");
                continue;
            }
            if(frm.equals( dest))
            {
                System.out.println("您输入的起点站和终点站是一个地铁站，不用坐地铁");
                continue;
            }
            int frmi = norm.get(frm);
            int to = norm.get(dest);
            SPFA(frmi);
            if(dist[to] >= INF)
            {
                System.out.println("您输入的起点站和终点站地铁不连通");
                continue;
            }
            int c = to;
            Stack<Integer> sta = new Stack<Integer>();
            while(upd[c] != -1)
            {
                sta.push(c);
                c = upd[c];
            }
            sta.push(frmi);
            while(!sta.empty())
            {
                int t = sta.pop();
                System.out.print(unnorm.get(t));
                System.out.print(" ");
            }
            System.out.println("");
        }
    }

}