133. Clone Graph

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# 題目敘述

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 value ( int ) and a list ( List[Node] ) of its neighbors.

class Node {
    public int val;
    public List<Node> neighbors;
}

Test case format:

For simplicity, each node's value is the same as the node's index (1-indexed). For example, the first node with val == 1 , the second node with val == 2 , and so on. The graph is represented in the test case using an adjacency list.

An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph.

The given node will always be the first node with val = 1 . You must return the copy of the given node as a reference to the cloned graph.

# Example 1:

Input: adjList = [[2,4],[1,3],[2,4],[1,3]]
Output: [[2,4],[1,3],[2,4],[1,3]]
Explanation: There are 4 nodes in the graph.
1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).
3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).

# Example 2:

Input: adjList = [[]]
Output: [[]]
Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors.

# Example 3:

Input: adjList = []
Output: []
Explanation: This an empty graph, it does not have any nodes.

# 解題思路

# Solution

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

// Definition for a Node.

class Node {

    public int val;

    public List<Node> neighbors;

    public Node() {

        val = 0;

        neighbors = new ArrayList<Node>();

    }

    public Node(int _val) {

        val = _val;

        neighbors = new ArrayList<Node>();

    }

    public Node(int _val, ArrayList<Node> _neighbors) {

        val = _val;

        neighbors = _neighbors;

    }

}

class Solution {

    Map<Node, Node> map = new HashMap<>();

    public Node cloneGraph(Node node) {

        if (node == null) return null;

        if (map.containsKey(node)) return map.get(node);

        map.put(node, new Node(node.val));

        for (Node val : node.neighbors) {

            map.get(node).neighbors.add(cloneGraph(val));

        }

        return map.get(node);

    }

}