LeetCode 133. Clone Graph（dfs）

最新推荐文章于 2021-07-14 09:59:19 发布

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最新推荐文章于 2021-07-14 09:59:19 发布

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分类专栏： LeetCode 文章标签： LeetCode Medium Java dfs

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本文介绍了一种使用深度优先搜索和HashMap实现无向图深拷贝的方法，针对LeetCode第133题Clone Graph。通过DFS遍历原图每个节点，同时在新图中创建对应的节点，并建立两图间节点的映射关系。

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题目来源：https://leetcode.com/problems/clone-graph/

问题描述

133. Clone Graph

Medium

Given a reference of a node in a connected undirected graph, return a deep copy (clone) of the graph. Each node in the graph contains a val (int) and a list (List[Node]) of its neighbors.

Example:

Input:

{"$id":"1","neighbors":[{"$id":"2","neighbors":[{"$ref":"1"},{"$id":"3","neighbors":[{"$ref":"2"},{"$id":"4","neighbors":[{"$ref":"3"},{"$ref":"1"}],"val":4}],"val":3}],"val":2},{"$ref":"4"}],"val":1}

Explanation:

Node 1's value is 1, and it has two neighbors: Node 2 and 4.

Node 2's value is 2, and it has two neighbors: Node 1 and 3.

Node 3's value is 3, and it has two neighbors: Node 2 and 4.

Node 4's value is 4, and it has two neighbors: Node 1 and 3.

Note:

The number of nodes will be between 1 and 100.
The undirected graph is a simple graph, which means no repeated edges and no self-loops in the graph.
Since the graph is undirected, if node p has node q as neighbor, then node q must have node p as neighbor too.
You must return the copy of the given node as a reference to the cloned graph.

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题意

给定一个节点，深拷贝节点所在的图。

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思路

深度优先搜索，用HashMap记录新图中已经生成的节点和原图中的节点的对应关系

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代码

/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> neighbors;

    public Node() {}

    public Node(int _val,List<Node> _neighbors) {
        val = _val;
        neighbors = _neighbors;
    }
};
*/
class Solution {
    private void dfs(Node root, Node node, HashMap<Node, Node> map) {
        for (Node neigh: node.neighbors) {
            if (map.containsKey(neigh)) {
                root.neighbors.add(map.get(neigh));
            } else {
                Node nroot = new Node(neigh.val, new ArrayList<Node>());
                map.put(neigh, nroot);
                dfs(nroot, neigh, map);
                root.neighbors.add(nroot);
            }
        }
    }
    
    public Node cloneGraph(Node node) {
        HashMap<Node, Node> map = new HashMap<Node, Node>();
        Node root = new Node(node.val, new ArrayList<Node>());
        map.put(node, root);
        dfs(root, node, map);
        return root;
    }
}