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Java-based LeetCode algorithm problem solutions, regularly updated
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package g0101_0200.s0133_clone_graph;

// #Medium #Hash_Table #Depth_First_Search #Breadth_First_Search #Graph #Udemy_Graph
// #2022_06_24_Time_45_ms_(29.80%)_Space_42.7_MB_(77.96%)

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

/**
 * 133 - Clone Graph\.
 *
 * Medium
 *
 * Given a reference of a node in a **[connected](https://en.wikipedia.org/wiki/Connectivity_(graph_theory)#Connected_graph)** undirected graph.
 *
 * Return a [**deep copy** ](https://en.wikipedia.org/wiki/Object_copying#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:**
 *
 * ![](https://assets.leetcode.com/uploads/2019/11/04/133_clone_graph_question.png)
 *
 * **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:**
 *
 * ![](https://assets.leetcode.com/uploads/2020/01/07/graph.png)
 *
 * **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:**
 *
 * ![](https://assets.leetcode.com/uploads/2020/01/07/graph-1.png)
 *
 * **Input:** adjList = \[\[2],[1]]
 *
 * **Output:** [[2],[1]] 
 *
 * **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.
**/
public class Solution {
    public Node cloneGraph(Node node) {
        return cloneGraph(node, new HashMap<>());
    }

    private Node cloneGraph(Node node, Map 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;
    }
}