題目描述(Medium)

Given the head of a graph, return a deep copy (clone) of the graph. Each node in the graph contains a label (int) and a list (List[UndirectedGraphNode]) of its neighbors. There is an edge between the given node and each of the nodes in its neighbors.

OJ's undirected graph serialization (so you can understand error output):

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
         / \
         \_/

Note

演算法分析

深搜，每個節點在鄰接節點列表中僅被標記一次，因此不會出現死迴圈。

提交程式碼：

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if(node == nullptr) return nullptr;
        unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> copy;
        dfs(node, copy);
        
        return copy[node];
    }
    
private:
    UndirectedGraphNode* dfs(UndirectedGraphNode *node, 
                              unordered_map<UndirectedGraphNode*, UndirectedGraphNode*>& copy) {
        
        if (copy.find(node) != copy.end()) return copy[node];
        UndirectedGraphNode *newNode = new UndirectedGraphNode(node->label);
        copy[node] = newNode;
        for (auto iter : node->neighbors)
            newNode->neighbors.push_back(dfs(iter, copy));
        return newNode;
    }
};