# 133 Clone Graph

## 133. Clone Graph

## 1. Question

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
         / \
         \_/
```

## 2. Implementation

**(1) BFS**

```java
/**
 * 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 null;
        }

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

        map.put(node, new UndirectedGraphNode(node.label));
        queue.add(node);

        while (!queue.isEmpty()) {
            UndirectedGraphNode curNode = queue.remove();

            for (UndirectedGraphNode nextNode : curNode.neighbors) {
                if (!map.containsKey(nextNode)) {
                    map.put(nextNode, new UndirectedGraphNode(nextNode.label));
                    queue.add(nextNode);
                }
                map.get(curNode).neighbors.add(map.get(nextNode));
            }
        }
        return map.get(node);
    }
}
```

**(2) DFS**

```java
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();

        return dfs(node, map);
    }

    public UndirectedGraphNode dfs(UndirectedGraphNode node, Map<UndirectedGraphNode, UndirectedGraphNode> map) {
        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 neighbor : node.neighbors) {
            copy.neighbors.add(dfs(neighbor, map));
        }
        return copy;
    }
}
```

## 3. Time & Space Complexity

BFS: 时间复杂度O(n), 空间复杂度O(n)

DFS: 时间复杂度O(n), 空间复杂度O(n)
