LeetCode-in-Java

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

class Node { public int val; public List 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.

Constraints:

• The number of nodes in the graph is in the range [0, 100].
• 1 <= Node.val <= 100
• Node.val is unique for each node.
• There are 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.

Solution

import com_github_leetcode.Node;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

public class Solution {
    public Node cloneGraph(Node node) {
        return cloneGraph(node, new HashMap<>());
    }

    private Node cloneGraph(Node node, Map<Node, Node> processedNodes) {
        if (node == null) {
            return null;
        } else if (processedNodes.get(node) != null) {
            return processedNodes.get(node);
        }
        Node newNode = new Node();
        processedNodes.put(node, newNode);
        newNode.val = node.val;
        newNode.neighbors = new ArrayList<>();
        for (Node neighbor : node.neighbors) {
            Node clonedNeighbor = cloneGraph(neighbor, processedNodes);
            if (clonedNeighbor != null) {
                newNode.neighbors.add(clonedNeighbor);
            }
        }
        return newNode;
    }
}