# Clone Graph

### 描述​

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbours.

OJ's undirected graph serialization: Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbour of the node. As an example, consider the serialized graph {0,1,2#1,2#2,2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

1. First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
2. Second node is labeled as 1. Connect node 1 to node 2.
3. Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.

Visually, the graph looks like the following:

       1      / \     /   \    0 --- 2         / \         \_/

### DFS​

// Clone Graph// DFS，时间复杂度O(n)，空间复杂度O(n)public class Solution {    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {        if(node == null) return null;        // key is original node，value is copied node        HashMap<UndirectedGraphNode, UndirectedGraphNode> visited = new HashMap<>();        clone(node, visited);        return visited.get(node);    }    // DFS    private static UndirectedGraphNode clone(UndirectedGraphNode node,                                              HashMap<UndirectedGraphNode,                                                      UndirectedGraphNode> visited) {        // a copy already exists        if (visited.containsKey(node)) return visited.get(node);        UndirectedGraphNode new_node = new UndirectedGraphNode(node.label);        visited.put(node, new_node);        for (UndirectedGraphNode nbr : node.neighbors)            new_node.neighbors.add(clone(nbr, visited));        return new_node;    }}

### BFS​

// Clone Graph// BFS，时间复杂度O(n)，空间复杂度O(n)public class Solution {    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {        if (node == null) return null;        // key is original node，value is copied node        HashMap<UndirectedGraphNode,UndirectedGraphNode> visited = new HashMap<>();        // each node in queue is already copied itself        // but neighbors are not copied yet        Queue<UndirectedGraphNode> q = new LinkedList<>();        q.offer(node);        visited.put(node, new UndirectedGraphNode(node.label));        while (!q.isEmpty()) {            UndirectedGraphNode cur = q.poll();            for (UndirectedGraphNode nbr : cur.neighbors) {                // a copy already exists                if (visited.containsKey(nbr)) {                    visited.get(cur).neighbors.add(visited.get(nbr));                } else {                    UndirectedGraphNode new_node =                            new UndirectedGraphNode(nbr.label);                    visited.put(nbr, new_node);                    visited.get(cur).neighbors.add(new_node);                    q.offer(nbr);                }            }        }        return visited.get(node);    }}