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133. Clone Graph.md

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leetcode-cn Daily Challenge on August 12th, 2020.

leetcode Daily Challenge on October 20th, 2020.


Difficulty : Medium

Related Topics : DFSBFSGraph


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.

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.

Example 1:

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:

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.

Example 4:

4

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

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

  • mine
    • Java
      • DFS Runtime: 26 ms, faster than 97.42%, Memory Usage: 39.9 MB, less than 50.09% of Java online submissions
        // O(N)time
        // O(N)space
        HashMap<Integer,Node> cache = new HashMap<>();
        
        public Node cloneGraph(Node node) {
            if(node == null) return node;
            dfs(node);
            return cache.get(node.val);
        }
        
        
        void dfs(Node node){
            if(cache.containsKey(node.val)){
                return;
            }
            Node copy = new Node(node.val);
            cache.put(node.val, copy);
            for(Node n : node.neighbors){
                dfs(n);
                copy.neighbors.add(cache.get(n.val));
            }
        }