[LeetCode] Clone Graph

Clone Graph

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
         / \
         \_/

解题思路：

题意为拷贝图。我们可以用一个map来存储新图的标签到节点指针的映射关系。同时，用一个队列来存储待确定邻居的节点（原图节点指针，因为我们通过指针标签很容易找到新图节点指针）。

/**
 * 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==NULL){
            return NULL;
        }
        map<int, UndirectedGraphNode*> nodeMap; //存的是新图的标签到节点指针对
        queue<UndirectedGraphNode*> nodeQ;      //存的是原图的节点指针
        
        UndirectedGraphNode* newNode = new UndirectedGraphNode(node->label);
        nodeMap[node->label] = newNode;
        nodeQ.push(node);
        
        while(!nodeQ.empty()){
            UndirectedGraphNode* n = nodeQ.front();
            nodeQ.pop();
            for(int i=0; i<n->neighbors.size(); i++){
                if(nodeMap.find(n->neighbors[i]->label) == nodeMap.end()){
                    nodeMap[n->neighbors[i]->label] = new UndirectedGraphNode(n->neighbors[i]->label);
                    nodeQ.push(n->neighbors[i]);
                }
                nodeMap[n->label]->neighbors.push_back(nodeMap[n->neighbors[i]->label]);
            }
        }
        
        return newNode;
    }
};