Wednesday, May 27, 2015

[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
         / \
         \_/
DFS : 
/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
private:
    typedef unordered_map<UndirectedGraphNode*,UndirectedGraphNode*> GraphMap;
    UndirectedGraphNode * clone(UndirectedGraphNode* node, GraphMap &map)
    {
        if(map.count(node)) return map[node];
        UndirectedGraphNode* newNode = new UndirectedGraphNode(node->label);
        map[node] = newNode;
        for(auto neighbor : node->neighbors)
        {
            UndirectedGraphNode* one = clone(neighbor, map);
            newNode->neighbors.push_back(one);
        }
        return newNode;
    }
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if(NULL == node) return NULL;
        GraphMap map;
        return clone(node, map);
    }
};
BFS : 
/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode *> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:    
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if(NULL == node) return NULL;
        queue<UndirectedGraphNode*> visit;
        GraphMap map;
        visit.push(node);
        UndirectedGraphNode * newCopy = new UndirectedGraphNode(node->label);
        map[node] = newCopy;
       
        while(!visit.empty())
        {
            UndirectedGraphNode *cur = visit.front();
            visit.pop();

            for(auto neighbor : cur->neighbors)
            {
                UndirectedGraphNode * newNeighbor;
                if(map.count(neighbor))
                {
                    newNeighbor = map[neighbor];
                }
                else
                {
                    newNeighbor = new UndirectedGraphNode(neighbor->label);
                    visit.push(neighbor);
                    map[neighbor] = newNeighbor;
                }
                map[cur]->neighbors.push_back(newNeighbor);
            }
        }
        
        return map[node];
    }
};
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