Java for LeetCode 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
         / \
         \_/
解题思路：

BFS或DFS均可做出，BFS的JAVA实现如下：

    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
		if (node == null)
			return null;
		Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
		HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
		UndirectedGraphNode newHead = new UndirectedGraphNode(node.label);
		queue.add(node);
		map.put(node, newHead);

		while (!queue.isEmpty()) {
			UndirectedGraphNode curr = queue.poll();
			List<UndirectedGraphNode> currNeighbors = curr.neighbors;
			for (UndirectedGraphNode aNeighbor : currNeighbors)
				if (!map.containsKey(aNeighbor)) {
					UndirectedGraphNode copy = new UndirectedGraphNode(
							aNeighbor.label);
					map.put(aNeighbor, copy);
					map.get(curr).neighbors.add(copy);
					queue.add(aNeighbor);
				} else
					map.get(curr).neighbors.add(map.get(aNeighbor));
		}
		return newHead;
    }

 DFS 实现如下：

	Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();

	public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
		if (node == null)
			return null;
		if (map.containsKey(node))
			return map.get(node);
		UndirectedGraphNode newHead = new UndirectedGraphNode(node.label);
		map.put(node, newHead);
		for (UndirectedGraphNode aNeighbor : node.neighbors)
			newHead.neighbors.add(cloneGraph(aNeighbor));
		return newHead;
	}