Clone Graph

这题第一眼看到想到的是BFS。接着想到我需要一个queue来做BFS。之后，为了能一一对应的复制，还用到一个Map。对应新旧node。

BUG： 就是我在复制新child node之前，就把旧child node添加到新的node的neighbors中了。

    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) {
            return null;
        }
        Queue<UndirectedGraphNode> q = new LinkedList<UndirectedGraphNode>();
        Map<UndirectedGraphNode,UndirectedGraphNode> map = new HashMap<UndirectedGraphNode,UndirectedGraphNode>();
        UndirectedGraphNode nodeCopy = new UndirectedGraphNode(node.label);
        q.add(node);
        map.put(node, nodeCopy);
        while (!q.isEmpty()) {
            UndirectedGraphNode cur = q.poll();
            UndirectedGraphNode curCopy = map.get(cur);
            for (UndirectedGraphNode child : cur.neighbors) {
                if (!map.containsKey(child)) {
                    UndirectedGraphNode childCopy = new UndirectedGraphNode(child.label);
                    map.put(child, childCopy);
                    q.offer(child);
                }
                //BUG：先复制child node
                curCopy.neighbors.add(map.get(child));
            }
        }
        return map.get(node);
    }