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 #.

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
     / \
     \_/

Tips:

先用bfs遍历取出所有节点存在Node里，然后map复制所有节点（不包括邻居），最后复制完成邻居。

可用BFS或DFS，我是用了BFS。先把所有点用BFS搞在ArrayList里，然后用map搞好，一一对应成新的，然后在把边搞了。

也有别的dfs和bfs的做法，都附上了。

Code：

解法1：自己的解法：

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) {
            return node;
        }
        HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
        ArrayList<UndirectedGraphNode> nodes = bfs(node);
        for (UndirectedGraphNode cur : nodes) {
            map.put(cur, new UndirectedGraphNode(cur.label));
        }
        for (UndirectedGraphNode cur: nodes) {
            UndirectedGraphNode newNode = map.get(cur);
            for (UndirectedGraphNode neighbor : cur.neighbors) {
                UndirectedGraphNode newNeighbor = map.get(neighbor);
                newNode.neighbors.add(newNeighbor);
            }
        }
        return map.get(node);
    }
    private ArrayList<UndirectedGraphNode> bfs(UndirectedGraphNode node) {
        ArrayList<UndirectedGraphNode> result = new ArrayList<>();
        Queue<UndirectedGraphNode> queue = new LinkedList<>();
        HashSet<UndirectedGraphNode> set = new HashSet<UndirectedGraphNode>();
        queue.add(node);
        set.add(node);
        while (!queue.isEmpty()) {
            UndirectedGraphNode cur = queue.remove();
            result.add(cur);
            for (UndirectedGraphNode neighbor : cur.neighbors) {
                if (!set.contains(neighbor)) {
                    queue.add(neighbor);
                    set.add(neighbor);
                }
            }
        }
        return result;
    }
}

解法2/3：

 private Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
// DFS
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
    if (node == null) return null;
    if (map.containsKey(node)) return map.get(node);
    UndirectedGraphNode copy = new UndirectedGraphNode(node.label);
    map.put(node, copy);
    for (UndirectedGraphNode n : node.neighbors)
        copy.neighbors.add(cloneGraph(n));
    return copy;
}

// BFS
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
    if (node == null) return null;
    Queue<UndirectedGraphNode> q = new LinkedList<UndirectedGraphNode>();
    q.add(node);
    UndirectedGraphNode copy = new UndirectedGraphNode(node.label);
    map.put(node, copy);
    while (!q.isEmpty()) {
        UndirectedGraphNode cur = q.poll();
        for (UndirectedGraphNode neigh : cur.neighbors) {
            if (map.containsKey(neigh)) map.get(cur).neighbors.add(map.get(neigh));
            else {
                UndirectedGraphNode neighCopy = new UndirectedGraphNode(neigh.label);
                map.put(neigh, neighCopy);
                map.get(cur).neighbors.add(neighCopy);
                q.add(neigh);
            }
        }
    }
    return copy;
}