# 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 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.


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.

## Solutions

• /*
// 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 {
private Map<Node, Node> visited = new HashMap<>();

public Node cloneGraph(Node node) {
if (node == null) {
return null;
}
if (visited.containsKey(node)) {
return visited.get(node);
}
Node clone = new Node(node.val);
visited.put(node, clone);
for (Node e : node.neighbors) {
}
return clone;
}
}

• /*
// Definition for a Node.
class Node {
public:
int val;
vector<Node*> neighbors;
Node() {
val = 0;
neighbors = vector<Node*>();
}
Node(int _val) {
val = _val;
neighbors = vector<Node*>();
}
Node(int _val, vector<Node*> _neighbors) {
val = _val;
neighbors = _neighbors;
}
};
*/

class Solution {
public:
unordered_map<Node*, Node*> visited;

Node* cloneGraph(Node* node) {
if (!node) return nullptr;
if (visited.count(node)) return visited[node];
Node* clone = new Node(node->val);
visited[node] = clone;
for (auto& e : node->neighbors)
clone->neighbors.push_back(cloneGraph(e));
return clone;
}
};

• """
# Definition for a Node.
class Node:
def __init__(self, val = 0, neighbors = None):
self.val = val
self.neighbors = neighbors if neighbors is not None else []
"""

class Solution:
def cloneGraph(self, node: 'Node') -> 'Node':
visited = defaultdict()

def clone(node):
if node is None:
return None
if node in visited:
return visited[node]
c = Node(node.val)
visited[node] = c
for e in node.neighbors:
c.neighbors.append(clone(e))
return c

return clone(node)


• /**
* Definition for a Node.
* type Node struct {
*     Val int
*     Neighbors []*Node
* }
*/

func cloneGraph(node *Node) *Node {
visited := map[*Node]*Node{}
var clone func(node *Node) *Node
clone = func(node *Node) *Node {
if node == nil {
return nil
}
if _, ok := visited[node]; ok {
return visited[node]
}
c := &Node{node.Val, []*Node{} }
visited[node] = c
for _, e := range node.Neighbors {
c.Neighbors = append(c.Neighbors, clone(e))
}
return c
}

return clone(node)
}

• /**
* Definition for Node.
* class Node {
*     val: number
*     neighbors: Node[]
*     constructor(val?: number, neighbors?: Node[]) {
*         this.val = (val===undefined ? 0 : val)
*         this.neighbors = (neighbors===undefined ? [] : neighbors)
*     }
* }
*/

function cloneGraph(node: Node | null): Node | null {
if (node == null) return null;

const visited = new Map();
visited.set(node, new Node(node.val));
const queue = [node];
while (queue.length) {
const cur = queue.shift();
for (let neighbor of cur.neighbors || []) {
if (!visited.has(neighbor)) {
queue.push(neighbor);
const newNeighbor = new Node(neighbor.val, []);
visited.set(neighbor, newNeighbor);
}
const newNode = visited.get(cur);
newNode.neighbors.push(visited.get(neighbor));
}
}
return visited.get(node);
}


• using System.Collections.Generic;

public class Solution {
public Node CloneGraph(Node node) {
if (node == null) return null;
var dict = new Dictionary<int, Node>();
var queue = new Queue<Node>();
queue.Enqueue(CloneVal(node));
while (queue.Count > 0)
{
var current = queue.Dequeue();
var newNeighbors = new List<Node>(current.neighbors.Count);
foreach (var oldNeighbor in current.neighbors)
{
Node newNeighbor;
if (!dict.TryGetValue(oldNeighbor.val, out newNeighbor))
{
newNeighbor = CloneVal(oldNeighbor);
queue.Enqueue(newNeighbor);
}
}
current.neighbors = newNeighbors;
}
return dict[node.val];
}

private Node CloneVal(Node node)
{
return new Node(node.val, new List<Node>(node.neighbors));
}
}