Clone Graph

• https://leetcode.com/problems/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 #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2. Second node is labeled as 1. Connect node 1 to node 2. Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.

DFS Solution

class UndirectedGraphNode {
    public int label;
    public List<UndirectedGraphNode> neighbors;
    public UndirectedGraphNode(int x) 
    { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
};

public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
    if (node == null) return null;

    Stack<Integer> visited = new Stack();
    UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);

    Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
    UndirectedGraphNode currentNode = newNode;

    HashMap<Integer, UndirectedGraphNode> map = new HashMap<Integer, UndirectedGraphNode>();

    queue.add(node);
    map.put(node.label, newNode);
    visited.add(node.label);

    while (!queue.isEmpty()) {
        UndirectedGraphNode visitingNode = queue.poll();
        currentNode = map.get(visitingNode.label);

        for (UndirectedGraphNode neighbor : visitingNode .neighbors) {
            if (!visited.contains(neighbor.label)) {
                UndirectedGraphNode tmpNode = new UndirectedGraphNode(neighbor.label);

                // mark the node as visited
                visited.add(neighbor.label);
                queue.offer(neighbor);

                currentNode.neighbors.add(tmpNode);

                if (!map.containsKey(neighbor.label))
                    map.put(neighbor.label, tmpNode);
            } else {
                currentNode.neighbors.add(map.get(neighbor.label));
            }
        }
    }
    return newNode;
}