单源最短路径Dijkstra和优先级算法

Posted 2021-02-08 674001396long

百度百科：迪杰斯特拉算法。

代码实现如下：

import java.util.Comparator;
import java.util.PriorityQueue;
import java.util.Scanner;

class Node
{
    int x;
    int value;
}
public class Main
{
    static int N,M,cnt;
    static final int MAX = 105;
    static final int INF = 1000009;
    static Node node[] = new Node[MAX];
    static int map[][] = new int[MAX][MAX];
    static int distence[] = new int[MAX];
    static boolean vis[] = new boolean[MAX];
    public static void main(String []args)
    {
        Scanner cin = new Scanner(System.in);
        while(cin.hasNext())
        {
            N = cin.nextInt();
            M = cin.nextInt();
            if(N == 0)
            {
                return;
            }
            cnt = 0;
            for(int i = 0; i < M; i++)
            {
                int a = cin.nextInt();
                int b = cin.nextInt();
                int c = cin.nextInt();
                map[a][b] = c;
                map[b][a] = c;
            }
            Dijkstra(N,M);
            for(int i = 1; i <= N; i++)
            {
                System.out.println(distence[i]);
            }
        }
    }
    static void Dijkstra(int N,int M)
    {
        Init();
        PriorityQueue <Node> que = new PriorityQueue<Node>(MAX,new Comparator<Node>()
                {
                    public int compare(Node o1, Node o2) 
                    {
                        if(o1.value > o2.value)
                        {
                            return 1;
                        }
                        else if(o1.value == o2.value)
                        {
                            return 0;
                        }
                        else
                        {
                            return -1;
                        }
                    }
                    
                });
        for(int i = 2; i <= N; i++)
        {
            if(map[1][i] != 0)
            {
                node[cnt].x = i;
                node[cnt].value = map[1][i];
                que.add(node[cnt]);
                cnt++;
            }
        }
        while(!que.isEmpty())
        {
            Node a = new Node();
            a = que.poll();
            if(vis[a.x] == true)
            {
                continue;
            }
            vis[a.x] = true;
            for(int i = 2; i <= N; i++)
            {
                if(vis[a.x] == false && distence[i] > distence[a.x]+map[a.x][i])
                {
                    distence[i] = distence[a.x]+map[a.x][i];
                    node[cnt].x = i;
                    node[cnt].value = map[a.x][i];
                    cnt++;
                }
            }
        }
    }
    static void Init()
    {
        node[0] = new Node();
        node[1] = new Node();
        for(int i = 2; i <= N; i++)
        {
            if(map[1][i] != 0)
            {
                distence[i] = map[1][i];
            }
            else
            {
                distence[i] = INF;
            }
            node[i] = new Node();
        }
    }
}