用Java语言编写贪心算法求解图的最短回路

以下是使用Java语言编写贪心算法求解图的最短回路的代码：

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.PriorityQueue;

public class ShortestCircuit {

    private int V;
    private ArrayList<ArrayList<Node>> adjList;

    public ShortestCircuit(int V) {
        this.V = V;
        adjList = new ArrayList<>();
        for (int i = 0; i < V; i++) {
            adjList.add(new ArrayList<>());
        }
    }

    public void addEdge(int u, int v, int w) {
        adjList.get(u).add(new Node(v, w));
        adjList.get(v).add(new Node(u, w));
    }

    public int shortestCircuit() {
        int[] dist = new int[V];
        Arrays.fill(dist, Integer.MAX_VALUE);
        PriorityQueue<Node> pq = new PriorityQueue<>(Comparator.comparingInt(node -> node.weight));

        // Set distance of source vertex to 0
        dist[0] = 0;
        pq.offer(new Node(0, 0));

        while (!pq.isEmpty()) {
            Node curr = pq.poll();
            int u = curr.vertex;

            for (Node neighbor : adjList.get(u)) {
                int v = neighbor.vertex;
                int w = neighbor.weight;

                if (dist[v] > dist[u] + w) {
                    dist[v] = dist[u] + w;
                    pq.offer(new Node(v, dist[v]));
                }
            }
        }

        int minCircuit = Integer.MAX_VALUE;
        for (int u = 0; u < V; u++) {
            for (Node neighbor : adjList.get(u)) {
                int v = neighbor.vertex;
                int w = neighbor.weight;

                if (dist[u] != Integer.MAX_VALUE && dist[v] != Integer.MAX_VALUE && minCircuit > dist[u] + w + dist[v]) {
                    minCircuit = dist[u] + w + dist[v];
                }
            }
        }

        return minCircuit;
    }

    private static class Node {
        int vertex;
        int weight;

        public Node(int vertex, int weight) {
            this.vertex = vertex;
            this.weight = weight;
        }
    }

    public static void main(String[] args) {
        ShortestCircuit g = new ShortestCircuit(4);
        g.addEdge(0, 1, 10);
        g.addEdge(1, 2, 20);
        g.addEdge(2, 3, 30);
        g.addEdge(3, 0, 40);

        int minCircuit = g.shortestCircuit();
        System.out.println("Minimum circuit length: " + minCircuit);
    }
}

在这个实现中，我们使用了优先队列来存储节点，以便按照距离顺序处理它们。我们还使用了邻接表来存储图形。对于每个节点，我们计算它到源节点的距离，并将其添加到优先队列中。然后，我们遍历所有边，计算每个环的长度，并返回最短环的长度。