Question

133. Clone Graph

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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

Solution 1

"""
# 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.
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) {
      clone.neighbors.add(cloneGraph(e));
    }
    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.
 * 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));
    dict.Add(node.val, queue.Peek());
    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);
          dict.Add(newNeighbor.val, newNeighbor);
        }
        newNeighbors.Add(newNeighbor);
      }
      current.neighbors = newNeighbors;
    }
    return dict[node.val];
  }

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