单源最短路径问题2 (Dijkstra算法)

用邻接矩阵

/*
单源最短路径问题2 (Dijkstra算法)
样例：
    5 7
    0 1 3
    0 3 7
    1 2 4
    1 3 2
    2 3 5
    2 4 6
    3 4 4
输出：
    [0, 3, 7, 5, 9]
*/

import java.util.Arrays;
import java.util.Scanner;

public class Main {
    //图的顶点数,总边数
    static int V, E;
    //存储所有的边,大小为顶点数
    static int[][] Edges;
    static int[] d;
    static boolean[] visited;
    static final int MAX_VALUE = 999999;

    public static void main(String[] args) {
        creatGraph();
        shortPath(1);
        System.out.println(Arrays.toString(d));
    }

    static void shortPath(int start) {
        d = new int[V];
        visited = new boolean[V];
        Arrays.fill(d, MAX_VALUE);
        d[start] = 0;
        while (true) {
            int min_index = -1;
            for (int j = 0; j < V; j++) {
                if (!visited[j] && (min_index == -1 || d[j] < d[min_index])) {
                    min_index = j;
                }
            }
            if (min_index == -1) break;
            visited[min_index] = true;
            for (int u = 0; u < V; u++) {
                d[u] = Math.min(d[u], d[min_index] + Edges[min_index][u]);
            }
        }
    }

    static void creatGraph() {
        Scanner sc = new Scanner(System.in);
        V = sc.nextInt();
        E = sc.nextInt();
        Edges = new int[V][V];
        for (int[] i : Edges)
            Arrays.fill(i, MAX_VALUE);
        for (int i = 0; i < E; i++) {
            int u = sc.nextInt();
            int v = sc.nextInt();
            int w = sc.nextInt();
            Edges[u][v] = w;
            Edges[v][u] = w;
        }
    }
}

用邻接表

/*
单源最短路径问题2 (Dijkstra算法)
样例：
    5 7
    0 1 3
    0 3 7
    1 2 4
    1 3 2
    2 3 5
    2 4 6
    3 4 4
输出：
    [0, 3, 7, 5, 9]
*/

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

public class Main {
    //图的顶点数,总边数
    static int V, E;
    //存储所有的边,大小为顶点数
    static ArrayList<Edge>[] Edges;
    static int[] d;
    static boolean[] visited;
    static final int MAX_VALUE = 999999;

    public static void main(String[] args) {
        creatGraph();
        shortPath(1);
        System.out.println(Arrays.toString(d));
    }

    static void shortPath(int start) {
        d = new int[V];
        visited = new boolean[V];
        Arrays.fill(d, MAX_VALUE);
        d[start] = 0;
        while (true) {
            int min_index = -1;
            for (int j = 0; j < V; j++) {
                if (!visited[j] && (min_index == -1 || d[j] < d[min_index])) {
                    min_index = j;
                }
            }
            if (min_index == -1) break;
            visited[min_index] = true;
            for (Edge i : Edges[min_index]) {
                d[i.to] = Math.min(d[i.to], d[min_index] + i.cost);
            }
        }
    }

    static void creatGraph() {
        Scanner sc = new Scanner(System.in);
        V = sc.nextInt();
        E = sc.nextInt();
        Edges = new ArrayList[V];
        for (int i = 0; i < V; i++)
            Edges[i] = new ArrayList();
        for (int i = 0; i < E; i++) {
            int u = sc.nextInt();
            int v = sc.nextInt();
            int w = sc.nextInt();
            Edges[u].add(new Edge(v, w));
            Edges[v].add(new Edge(u, w));
        }
    }
}

class Edge {
    int to;
    int cost;

    public Edge(int to, int cost) {
        this.to = to;
        this.cost = cost;
    }
}