【Lintcode】137.Clone Graph

题目：

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.

How we serialize an undirected graph:

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
     / 
     \_/

Example

return a deep copied graph.

题解：

　　DFS(recursion)

Solution 1 ()

class Solution {
public:
    unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> hash;
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
       if (!node) return node;
       if(hash.find(node) == hash.end()) {
           hash[node] = new UndirectedGraphNode(node -> label);
           for (auto neighbor : node -> neighbors) {
                (hash[node] -> neighbors).push_back( cloneGraph(neighbor) );
           }
       }
       return hash[node];
    }
};

　　DFS(stack)

Solution 2 ()

class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (node == nullptr) 
            return nullptr;
        stack<UndirectedGraphNode* > stack;
        
        map<int, UndirectedGraphNode* > visitTable;
        UndirectedGraphNode* newnode = new UndirectedGraphNode(node->label);
        visitTable[node->label] = newnode;
        stack.push(node);
        
        while (!stack.empty()) {
            UndirectedGraphNode* cur = stack.top();
            stack.pop();
            for (auto neighbor : cur->neighbors) {
                if (visitTable.find(neighbor->label) == visitTable.end()) {
                    stack.push(neighbor);
                    UndirectedGraphNode* newneighbor = new UndirectedGraphNode(neighbor->label);
                    visitTable[neighbor->label] = newneighbor;
                }
                visitTable[cur->label]->neighbors.push_back(visitTable[neighbor->label]);
            }
        }
        
        return newnode;
    }
};

　　BFS

Solution 3 ()

class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (node == nullptr) 
            return nullptr;
        queue<UndirectedGraphNode* > queue;
        
        map<int, UndirectedGraphNode* > visitTable;
        UndirectedGraphNode* newnode = new UndirectedGraphNode(node->label);
        visitTable[node->label] = newnode;
        queue.push(node);
        
        while (!queue.empty()) {
            UndirectedGraphNode* cur = queue.front();
            queue.pop();
            for (auto neighbor : cur->neighbors) {
                if (visitTable.find(neighbor->label) == visitTable.end()) {
                    UndirectedGraphNode* newneighbor = new UndirectedGraphNode(neighbor->label);
                    visitTable[neighbor->label] = newneighbor;
                    queue.push(neighbor);
                }
                visitTable[cur->label]->neighbors.push_back(visitTable[neighbor->label]);
            }
        }
        
        return newnode;
    }
};