133

133. Clone Graph (Medium)

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.

Companies:
Facebook, Amazon, Microsoft, Google, Bloomberg, Salesforce, Twitter, Oracle

Related Topics:
Hash Table, Depth-First Search, Breadth-First Search, Graph

Similar Questions:

• Copy List with Random Pointer (Medium)
• Clone Binary Tree With Random Pointer (Medium)
• Clone N-ary Tree (Medium)

Solution 1. DFS

An unordered_map is used to record the mapping between the original and copied nodes, and to ensure each node is only copied once.

// OJ: https://leetcode.com/problems/clone-graph/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
    unordered_map<Node*, Node*> m;
public:
    Node* cloneGraph(Node* node) {
        if (!node) return nullptr;
        if (m.count(node)) return m[node];
        auto cpy = new Node(node->val);
        m[node] = cpy;
        for (auto &n : node->neighbors) cpy->neighbors.push_back(cloneGraph(n));
        return cpy;
    }
};

Solution 2. BFS

// OJ: https://leetcode.com/problems/clone-graph/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
public:
    Node* cloneGraph(Node* node) {
        if (!node) return nullptr;
        queue<Node*> q;
        unordered_map<Node*, Node*> m;
        m[node] = new Node(node->val);
        q.push(node);
        while (q.size()) {
            auto p = q.front();
            q.pop();
            auto copy = m[p];
            for (auto nei : p->neighbors) {
                if (!m.count(nei)) {
                    m[nei] = new Node(nei->val);
                    q.push(nei);
                }
                copy->neighbors.push_back(m[nei]);
            }
        }
        return m[node];
    }
};