LeetCode 133 - 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
         / \
         \_/

Solution 1:

BFS

public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
    if(node == null) return null;
    Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
    UndirectedGraphNode cloned = new UndirectedGraphNode(node.label);
    map.put(node,cloned);
    Queue<UndirectedGraphNode> queue = new LinkedList<>();
    queue.offer(node);
    while(!queue.isEmpty()) {
        UndirectedGraphNode u = queue.poll();
        UndirectedGraphNode v = map.get(u);
        for(UndirectedGraphNode n: u.neighbors) {
            UndirectedGraphNode copied = map.get(n);
            if(copied == null) {
                copied = new UndirectedGraphNode(n.label);
                map.put(n, copied);
                queue.offer(n);
            }
            v.neighbors.add(copied);
        }
    }
    return cloned;
}

UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
    if(!node) return nullptr;
    queue<UndirectedGraphNode*> q;
    unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> gmap;
    gmap[node] = new UndirectedGraphNode(node->label);
    q.push(node);
    while(!q.empty()) {
        UndirectedGraphNode *n = q.front();
        q.pop();
        for(auto neighbor:n->neighbors) {
            if(gmap.count(neighbor) == 0) {
                gmap[neighbor] = new UndirectedGraphNode(neighbor->label);
                q.push(neighbor);
            } 
            gmap[n]->neighbors.push_back(gmap[neighbor]);
        }
    }
    return gmap[node];
}

   

Solution 2:

DFS

private Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
    if(node == null) return null;
    UndirectedGraphNode clonedNode = new UndirectedGraphNode(node.label);
    List<UndirectedGraphNode> neighbors = clonedNode.neighbors;
    
    for(UndirectedGraphNode n:node.neighbors) {
        if(n.label == node.label) {
            neighbors.add(clonedNode);
            continue;
        }
        if(map.containsKey(n)) {
            neighbors.add(map.get(n));
        } else {
            UndirectedGraphNode value = cloneGraph(n);
            neighbors.add(value);
            map.put(n, value);
        }
    }
    return clonedNode;
}

unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> gmap;
UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
    if(!node) return nullptr;
    if(gmap.count(node) == 0) {
        gmap[node] = new UndirectedGraphNode(node->label);
        for(auto neighbor:node->neighbors) {
            gmap[node]->neighbors.push_back(cloneGraph(neighbor));
        }
    }
    return gmap[node];
}