Clone Graph Leetcode Solution

In this post, we are going to solve the Clone Graph Leetcode Solution problem of Leetcode. This Leetcode problem is done in many programming languages like C++, Java, and Python.

Clone Graph Leetcode Solution
Clone Graph Leetcode Solution


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 nodes 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:

Clone Graph Leetcode Solution
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:

Clone Graph Leetcode Solution
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.


  • 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.

Now, lets see the leetcode solution of Clone Graph Leetcode Solution.

Clone Graph Leetcode Solution in Python

class Solution:
  def cloneGraph(self, node: 'Node') -> 'Node':
    if not node:
      return None

    q = deque([node])
    map = {node: Node(node.val)}

    while q:
      u = q.popleft()
      for v in u.neighbors:
        if v not in map:
          map[v] = Node(v.val)

    return map[node]

Clone Graph Leetcode Solution in CPP

class Solution {
  Node* cloneGraph(Node* node) {
    if (node == nullptr)
      return nullptr;

    queue<Node*> q{{node}};
    unordered_map<Node*, Node*> map{{node, new Node(node->val)}};

    while (!q.empty()) {
      Node* u = q.front();
      for (Node* v : u->neighbors) {
        if (!map.count(v)) {
          map[v] = new Node(v->val);

    return map[node];

Clone Graph Leetcode Solution in Java

class Solution {
  public Node cloneGraph(Node node) {
    if (node == null)
      return null;

    Queue<Node> q = new ArrayDeque<>(Arrays.asList(node));
    Map<Node, Node> map = new HashMap<>();
    map.put(node, new Node(node.val));

    while (!q.isEmpty()) {
      Node u = q.poll();
      for (Node v : u.neighbors) {
        if (!map.containsKey(v)) {
          map.put(v, new Node(v.val));

    return map.get(node);

Note: This problem Clone Graph is generated by Leetcode but the solution is provided by Chase2learn This tutorial is only for Educational and Learning purpose.

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