leetcode 133: Clone Graph

最新推荐文章于 2021-12-18 21:11:27 发布

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本文介绍了如何使用BFS遍历并利用哈希表存储已创建节点来避免重复创建相同标签的节点，在无向图复制过程中优化节点创建逻辑。

Not a hard problem, just the details are a little tricky to think. I used the queue to BFS, while doing it, I used the unordered set and unordered map to save the nodes that are already been created. Whenever a node is created before, you shouldn't create a new one with the same label.

/**
 * 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)
            return NULL;
        queue<UndirectedGraphNode*> qold;//queue for the original graph
        queue<UndirectedGraphNode*> qnew;//queue for the new graph
        unordered_set<UndirectedGraphNode*> oldset;//save all nodes that are existed
        unordered_map<int,UndirectedGraphNode*> newset;
        qold.push(node);
        UndirectedGraphNode* pbegin=new UndirectedGraphNode(node->label);
        qnew.push(pbegin);
        while(!qold.empty())
        {
            UndirectedGraphNode* pold=qold.front();
            qold.pop();
            UndirectedGraphNode* pnew=qnew.front();
            qnew.pop();
            if(oldset.find(pold)==oldset.end())//make this node existed if not
            {
                oldset.insert(pold);
                newset.insert(make_pair(pnew->label,pnew));
            }
            for(int i=0;i<pold->neighbors.size();i++)
            {
                if(oldset.find(pold->neighbors[i])!=oldset.end())//the neighbor i is an existed node
                {
                    UndirectedGraphNode* ptemp=newset[pold->neighbors[i]->label];//find the existed node's address through label
                    pnew->neighbors.push_back(ptemp);
                }
                else
                {
                    UndirectedGraphNode* ptemp=new UndirectedGraphNode(pold->neighbors[i]->label);
                    pnew->neighbors.push_back(ptemp);
                    qold.push(pold->neighbors[i]);
                    qnew.push(ptemp);
                    oldset.insert(pold->neighbors[i]);
                    newset.insert(make_pair(pold->neighbors[i]->label,ptemp));
                }
            }
        }
        return pbegin;
    }
};