Clone Graph 题解

题目来源：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 #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
Second node is labeled as 1. Connect node 1 to node 2.
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
         / \
         \_/

解题思路：

用BFS+hashmap解决。

    //Definition for undirected graph.
    struct UndirectedGraphNode 
    {
        int label;
        vector<UndirectedGraphNode *> neighbors;
        UndirectedGraphNode(int x) : label(x) {};
    };

    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) 
    {
        if(node == NULL) return NULL;
        unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> copies;
        queue<UndirectedGraphNode*> todo; 
        todo.push(node);
        copies[node] = new UndirectedGraphNode(node->label);
        while(!todo.empty())
        {
            auto origin = todo.front(); todo.pop();
            UndirectedGraphNode* cpy = copies[origin];
            for(auto it = origin->neighbors.begin(); it != origin->neighbors.end(); it++)
            {
                if(copies.find(*it) == copies.end())
                {
                    auto node1 = new  UndirectedGraphNode((*it)->label);    
                    copies[*it] = node1;
                    todo.push(*it);
                }
                cpy->neighbors.push_back(copies[*it]);
            }
        }
        return copies[node];
    }