[Java]LeetCode133. 克隆图 | Clone Graph

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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
         / 
         \_/

---

克隆一张无向图，图中的每个节点包含一个 label （标签）和一个 neighbors （邻接点）列表 。

OJ的无向图序列化：

节点被唯一标记。

我们用 # 作为每个节点的分隔符，用 , 作为节点标签和邻接点的分隔符。

例如，序列化无向图 {0,1,2#1,2#2,2}。

该图总共有三个节点, 被两个分隔符  # 分为三部分。 

1. 第一个节点的标签为 0，存在从节点 0 到节点 1 和节点 2 的两条边。
2. 第二个节点的标签为 1，存在从节点 1 到节点 2 的一条边。
3. 第三个节点的标签为 2，存在从节点 2 到节点 2 (本身) 的一条边，从而形成自环。

我们将图形可视化如下：

       1
      / 
     /   
    0 --- 2
         / 
         \_/

---

2ms

/**
 * 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<Integer, UndirectedGraphNode> map = new HashMap<>();  // 存放节点
        return dfs(map, node);
    }
    
     private  UndirectedGraphNode dfs(Map<Integer, UndirectedGraphNode> map, UndirectedGraphNode node) {
        // 是否存在 存在返回
        UndirectedGraphNode cloned = map.get(node.label);
        if (cloned != null) return cloned;
        // clone一个
        cloned = new UndirectedGraphNode(node.label);
        map.put(cloned.label, cloned);
        // 加入子节点
        for(UndirectedGraphNode neighbor: node.neighbors) {
            cloned.neighbors.add(dfs(map,neighbor));
        }
        return cloned;
    }
}

---

2ms

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    HashMap<Integer, UndirectedGraphNode> map = new HashMap<>();
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if(node==null)
            return null;
        
        UndirectedGraphNode head = new UndirectedGraphNode(node.label);
        map.put(head.label, head);
       
        for(UndirectedGraphNode nei: node.neighbors) {
            // UndirectedGraphNode nei1 = null;
            UndirectedGraphNode nei1 = map.get(nei.label);
            if(nei1==null) {
                head.neighbors.add(cloneGraph(nei));
            }
            else
                head.neighbors.add(nei1);
        }
        return head;
    }
}

---

4ms

/**
 * 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> visited = new HashMap<>();
        visited.put(node, new UndirectedGraphNode(node.label));
        dfs(node, visited);
        return visited.get(node);
    }
    
    private void dfs(UndirectedGraphNode node, Map<UndirectedGraphNode, UndirectedGraphNode> visited) {
        for (UndirectedGraphNode nei : node.neighbors) {
            if (!visited.containsKey(nei)) {
                visited.put(nei, new UndirectedGraphNode(nei.label));
                dfs(nei, visited);
            }
            visited.get(node).neighbors.add(visited.get(nei));
        }    
    
    }
}

---

5ms

/**
 * 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<Integer, UndirectedGraphNode> valToNode = new HashMap<>();
        Queue<UndirectedGraphNode> queue = new LinkedList<>();
        queue.add(node);
        
        while(!queue.isEmpty()){
            UndirectedGraphNode current = queue.poll();
            UndirectedGraphNode copiedNode = valToNode.getOrDefault(current.label, new UndirectedGraphNode(current.label));
            valToNode.put(current.label, copiedNode);
            
            for(UndirectedGraphNode neighbor : current.neighbors){
                UndirectedGraphNode copiedNeighbor = valToNode.getOrDefault(neighbor.label, new UndirectedGraphNode(neighbor.label));
                copiedNode.neighbors.add(copiedNeighbor);
                
                if(!valToNode.containsKey(neighbor.label)){
                    queue.add(neighbor);
                    valToNode.put(neighbor.label, copiedNeighbor);
                }
            }
        }
        
        return valToNode.get(node.label);
    }
}