LeetCode 133. Clone Graph

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

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 node0 to both nodes 1 and2.
2. Second node is labeled as 1. Connect node1 to node 2.
3. Third node is labeled as 2. Connect node2 to node 2 (itself), thus forming a self-cycle.

Visually, the graph looks like the following:

       1
      / \
     /   \
    0 --- 2
         / \
         \_/

When comes to graph, usually comes with a mess. Actually graph is not that complicated.

This problem is a good one to dissolve the fear.

    // this is to use BFS.
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if(!node) return NULL;
        unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> hashMap;
        hashMap.insert({node, new UndirectedGraphNode(node->label)});
        queue<UndirectedGraphNode*> nodes;
        nodes.push(node);
        while(!nodes.empty()) {
            auto v = nodes.front();
            nodes.pop();
            for(UndirectedGraphNode* e : v->neighbors) {
                if(hashMap.find(e) == hashMap.end()) {
                    hashMap.insert({e,  new UndirectedGraphNode(e->label)});
                    nodes.push(e);
                }
                (hashMap[v]->neighbors).push_back(hashMap[e]);
            }
        }
        return hashMap[node];
    }

It can also be done using dfs.

void dfs(unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> hashMap, UndirectedGraphNode* node) {
  if(!node) return;
  for(auto e : node->neighbors) {
    if(hashMap.find(e) == hashMap.end()) {
      hashMap[e] = new UndirectedGraphNode(e->val);
      dfs(hashMap, e);
    }
    hashMap[e]->neighbors.push_back(hashMap[e]);
  }
}

UndirectedGraphNode* cloneGraph(UndirectedGraphNode* node) {
  if(!root) return NULL;
  unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> hashMap;
  UndirectedGraphNod* head = new UndirectedGraphNode(node->val);
  hashMap.insert({node, head});
  dfs(hashMap, node);
  return head;
}