Clone Graph -- LeetCode

Posted 2020-08-04 Coder and Writer

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。

 1 /**
 2  * Definition for undirected graph.
 3  * struct UndirectedGraphNode {
 4  *     int label;
 5  *     vector<UndirectedGraphNode *> neighbors;
 6  *     UndirectedGraphNode(int x) : label(x) {};
 7  * };
 8  */
 9 class Solution {
10 public:
11     //suppose these two node are already labelled
12     void help(UndirectedGraphNode *originalNode, UndirectedGraphNode *copiedNode, unordered_map<int, UndirectedGraphNode*> &dict) {
13         for (int i = 0; i < originalNode->neighbors.size(); i++) {
14             int childLabel = originalNode->neighbors[i]->label;
15             if (dict.count(childLabel) > 0) copiedNode->neighbors.push_back(dict[childLabel]);
16             else {
17                 UndirectedGraphNode *node = new UndirectedGraphNode(childLabel);
18                 dict.insert(make_pair(childLabel, node));
19                 copiedNode->neighbors.push_back(node);
20                 help(originalNode->neighbors[i], node, dict);
21             }
22         }
23     }
24     UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
25         if (node == NULL) return NULL;
26         unordered_map<int, UndirectedGraphNode*> dict;
27         UndirectedGraphNode *copiedNode = new UndirectedGraphNode(node->label);
28         dict.insert(make_pair(node->label, copiedNode));
29         help(node, copiedNode, dict);
30         return copiedNode;
31     }
32 };