[LeetCode] 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
         / \
         \_/

思路

和Copy List with Random Pointer那题的思路一样。用一个hash table记录原图节点和复制图节点间的对应关系，以防止重复建立节点。和那题的不同在于遍历原图相对比linked list的情况复杂一点。可以用BFS或DFS来遍历原图。而hash table本身除了记录对应关系外，还有记录原图中每个节点是否已经被visit的功能。

BFS遍历：

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

class Solution { public: UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) { if(!node) return NULL; UndirectedGraphNode *p1 = node; UndirectedGraphNode *p2 = new UndirectedGraphNode(node->label); unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> ht; queue<UndirectedGraphNode*> q; q.push(node); ht[node] = p2; while(!q.empty()) { p1 = q.front(); p2 = ht[p1]; q.pop(); for(int i=0; i<p1->neighbors.size(); i++) { UndirectedGraphNode *nb = p1->neighbors[i]; if(ht.count(nb)) { p2->neighbors.push_back(ht[nb]); } else { UndirectedGraphNode *temp = new UndirectedGraphNode(nb->label); p2->neighbors.push_back(temp); ht[nb] = temp; q.push(nb); } } } return ht[node]; } };

DFS遍历：

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

class Solution { public: UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) { if(!node) return NULL; unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> ht; stack<UndirectedGraphNode*> s; s.push(node); ht[node] = new UndirectedGraphNode(node->label); while(!s.empty()) { UndirectedGraphNode *p1 = s.top(), *p2 = ht[p1]; s.pop(); for(int i=0; i<p1->neighbors.size(); i++) { UndirectedGraphNode *nb = p1->neighbors[i]; if(ht.count(nb)) { p2->neighbors.push_back(ht[nb]); } else { UndirectedGraphNode *temp = new UndirectedGraphNode(nb->label); p2->neighbors.push_back(temp); ht[nb] = temp; s.push(nb); } } } return ht[node]; } };