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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

Solution 1

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"""
# 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)

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/*
// 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;
    }
}

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/*
// 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;
    }
};

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/**
 * 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)
}

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/**
 * 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);
}

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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));
    }
}

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