133. Clone Graph

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 val (int) and a list (List[Node]) of its neighbors.

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class Node {
    public int val;
    public List<Node> neighbors;
}

Test case format:

For simplicity sake, 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.

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.

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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).

ex1

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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.

ex1

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Example 3:

Input: adjList = []
Output: []
Explanation: This an empty graph, it does not have any nodes.

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Example 4:

Input: adjList = [[2],[1]]
Output: [[2],[1]]

ex4

Constraints:

  • 1 <= Node.val <= 100
  • Node.val is unique for each node.
  • Number of Nodes will not exceed 100.
  • There is 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.

Solution

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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 {
    Node[] map = new Node[101];
    public Node cloneGraph(Node node) {
        if (node == null) return null;
        
        if (map[node.val] != null) {
            return map[node.val];
        }
        Node clone = new Node(node.val);
        map[clone.val] = clone;
        
        for (Node n: node.neighbors) {
            clone.neighbors.add(cloneGraph(n));
        }
        
        return clone;
    }
}

Solution 2021-11-22

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class Solution {
    Map<Integer, Node> cache = new HashMap<>();
    public Node cloneGraph(Node node) {
        if (node == null) return null;
        
        Node curr = cache.get(node.val);
        if (curr != null) return curr;
        
        curr = new Node(node.val);
        cache.put(curr.val, curr);
        
        for (Node nei: node.neighbors) {
            curr.neighbors.add(cloneGraph(nei));
        }
                     
        return curr;
    }
}

Solution 2022-01-30

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class Solution {
    Map<Integer, Node> cache = new HashMap<>();
    public Node cloneGraph(Node node) {
        if (node == null) return null;
        if (cache.containsKey(node.val)) {
            return cache.get(node.val);
        }
        Node newNode = new Node(node.val);
        cache.put(newNode.val, newNode);
        for (Node nei: node.neighbors) {
            newNode.neighbors.add(cloneGraph(nei));
        }
        return newNode;
    }
}