133. Clone Graph

Description

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.

Test case format:

For simplicity sake, 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.

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.

Constraints

• 1 <= Node.val <= 100

• Node.val is unique for each node.

• Number of Nodes will not exceed 100.

• There is no repeated edges and no self-loops in the graph.

• The Graph is connected and all nodes can be visited starting from the given node.

Approach

Links

• GeeksforGeeks
• Leetcode
• ProgramCreek
• YouTube

Examples

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.

Example 4

Input: adjList = [[2], [1]]

Output: [[2], [1]]

Solutions

Node

// 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;
    }
}

Solution 1

/**
 * Time complexity : 
 * Space complexity : 
 */

class Solution {
    public Node cloneGraph(Node node) {
        if(node == null) return null;
        Map<Integer, Node> nodes = new HashMap();
        return helper(node, nodes);
    }
    
    private Node helper(Node node, Map<Integer, Node> nodes) {
        if(node == null) return null;
        
        if(nodes.containsKey(node.val)) {
            return nodes.get(node.val);
        }
        
        Node newNode = new Node(node.val);
        nodes.put(node.val, newNode);
        for(Node neighbor: node.neighbors) {
            newNode.neighbors.add(helper(neighbor, nodes));
        }
        return newNode;
    }
}

Solution 2

/**
 * Time complexity : 
 * Space complexity : 
 */
 
class Solution {
    
    private Map<Integer, Node> nodes = new HashMap<>();
    
    public Node cloneGraph(Node node) {
        if(node == null) return null;
        
        if(nodes.containsKey(node.val)) {
            return nodes.get(node.val);
        }
        
        Node newNode = new Node(node.val);
        nodes.put(node.val, newNode);
        
        for(Node adj: node.neighbors) {
            newNode.neighbors.add(cloneGraph(adj));
        }
        
        return newNode;
    }
}

Follow up