克隆图

/*
 * Problem Description:
 * You are given a reference of a node in a connected undirected graph, 
 * and you need to return a deep copy (clone) of the graph.
 * Each node contains a value (int) and a list of its neighbors.
 * The graph is represented as an adjacency list in the test cases.
 */
 
import java.util.*;
import java.util.stream.*;
 
class Node {
    public int val;
    public List<Node> neighbors;
    public Node(int val) {
        this.val = val;
        this.neighbors = new ArrayList<>();
    }
}
 
public class Solution {
    // HashMap to store the mapping from original node to its clone
    private Map<Node, Node> visited = new HashMap<>();
    
    // Method to clone the graph using Java Stream
    public Node cloneGraph(Node node) {
        if (node == null) return null;
        // If the node is already cloned, return the clone
        if (visited.containsKey(node)) return visited.get(node);
        // Create a new node for the clone
        Node cloneNode = new Node(node.val);
        // Store the clone in the visited map
        visited.put(node, cloneNode);
        // Clone neighbors using Stream API
        cloneNode.neighbors = node.neighbors.stream()
                                  .map(this::cloneGraph)
                                  .collect(Collectors.toList());
        return cloneNode;
    }
}