【leetcode】Clone Graph

链接：https://oj.leetcode.com/problems/clone-graph/

描述:

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         / \         \_/

方法一：

类似前面Random List copy思路，三遍遍历，第一遍针对原始的图中的每一个节点复制一个放在该节点的最后neighbour，第二遍将所有的节点的邻居修改为正确的，最后一遍从原来的图节点剥离新的节点。

超时。

代码如下：

UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {if( node == NULL) return NULL;UndirectedGraphNode *p = node;set<UndirectedGraphNode*> visitNode;queue<UndirectedGraphNode*> q;q.push(node);while(!q.empty()){p = q.front();q.pop();visitNode.insert(p);vector<UndirectedGraphNode*>::iterator it = p->neighbors.begin();while( it != p->neighbors.end() ){if(visitNode.count(*it) <= 0)q.push(*it);it++;}UndirectedGraphNode* newNode = new UndirectedGraphNode(p->label);newNode->neighbors = p->neighbors;p->neighbors.push_back(newNode);}set<UndirectedGraphNode*>::iterator itSet = visitNode.begin();while( itSet != visitNode.end() ){p = (*itSet)->neighbors.back();vector<UndirectedGraphNode*> newNei;vector<UndirectedGraphNode*>::iterator itV = p->neighbors.begin();while( itV != p->neighbors.end() ){newNei.push_back((*itV)->neighbors.back());itV++;}p->neighbors = newNei;itSet++;}itSet = visitNode.begin();UndirectedGraphNode * result = (*itSet)->neighbors.back();while( itSet != visitNode.end() ){(*itSet)->neighbors.pop_back();itSet++;}return result;}

方法二：

只需要一次遍历，BFS遍历，在每次入栈之前对每一个原图节点新建一个节点，保存新节点和原来节点的关系，在每一次出队列时对新的节点设置neighbous。

借助hash加速。

代码如下：

UndirectedGraphNode* cloneGraphMap(UndirectedGraphNode *node){if( node == NULL) return NULL;map<UndirectedGraphNode*, UndirectedGraphNode*> nodeMap;queue<UndirectedGraphNode*> q;q.push(node);nodeMap[node] = new UndirectedGraphNode(node->label);while(!q.empty()){UndirectedGraphNode *p = q.front();q.pop();UndirectedGraphNode *copy = nodeMap[p];vector<UndirectedGraphNode*>::iterator it = p->neighbors.begin();while( it != p->neighbors.end() ){if( nodeMap.count(*it) <= 0){nodeMap[*it] = new UndirectedGraphNode((*it)->label);q.push(*it);}copy->neighbors.push_back(nodeMap[*it]);it++;}}return nodeMap[node];}