Clone Graph -- LeetCode

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
         / 
         \_/

思路：DFS。

要点：用一个map记录所有的label与指针的pair。这样可以避免环以及创建重复的节点。

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    //suppose these two node are already labelled
    void help(UndirectedGraphNode *originalNode, UndirectedGraphNode *copiedNode, unordered_map<int, UndirectedGraphNode*> &dict) {
        for (int i = 0; i < originalNode->neighbors.size(); i++) {
            int childLabel = originalNode->neighbors[i]->label;
            if (dict.count(childLabel) > 0) copiedNode->neighbors.push_back(dict[childLabel]);
            else {
                UndirectedGraphNode *node = new UndirectedGraphNode(childLabel);
                dict.insert(make_pair(childLabel, node));
                copiedNode->neighbors.push_back(node);
                help(originalNode->neighbors[i], node, dict);
            }
        }
    }
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (node == NULL) return NULL;
        unordered_map<int, UndirectedGraphNode*> dict;
        UndirectedGraphNode *copiedNode = new UndirectedGraphNode(node->label);
        dict.insert(make_pair(node->label, copiedNode));
        help(node, copiedNode, dict);
        return copiedNode;
    }
};