133. Clone Graph

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

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 neighbor 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 #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
Second node is labeled as 1. Connect node 1 to node 2.
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
         / \
         \_/

思路:图的基础题目, 用DFS或者BFS 来做。
要利用HashMap来建立个从原节点到克隆节点的map,用来判断我们是否克隆过某个节点。

DFS:

public class Solution {
    HashMap<Integer, UndirectedGraphNode> map = new HashMap<>();
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) return node;
        if (map.containsKey(node.label)) 
            return map.get(node.label);
        // init the clone node
        UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);
        map.put(node.label, newNode);
        // iterate origin node's neighbor and clone it
        for (UndirectedGraphNode n: node.neighbors) {
            newNode.neighbors.add(cloneGraph(n));
        }
        return newNode;
    }
}

BFS:

public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) return node;
        HashMap<Integer, UndirectedGraphNode> visited = new HashMap<>();
        Deque<UndirectedGraphNode> queue = new ArrayDeque<>();
        UndirectedGraphNode newNode= new UndirectedGraphNode(node.label);
        visited.put(node.label, newNode);
        queue.offer(node);
        while(!queue.isEmpty()) {
            UndirectedGraphNode cur = queue.poll();
            for (UndirectedGraphNode n : cur.neighbors) {
                if (!visited.containsKey(n.label)) {
                    queue.offer(n);
                    visited.put(n.label, new UndirectedGraphNode(n.label));
                }
                visited.get(cur.label).neighbors.add(visited.get(n.label));
            }
        }
        return visited.get(node.label);
    }
}
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