Clone Graph

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: BFS遍历图 用Hash表存储Original Node-》 Copy Node 映射
O(n) time complexity, O(n) space

public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
    if (node == null) {
        return null;
    }
    Queue<UndirectedGraphNode> queue = new LinkedList<>();
    Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
    queue.offer(node);
    UndirectedGraphNode copyRoot = new UndirectedGraphNode(node.label);
    map.put(node, copyRoot);
    while (!queue.isEmpty()) {
        int count = queue.size();
        for (int i = 0; i < count; i++) {
            UndirectedGraphNode curr = queue.poll();
            for (UndirectedGraphNode neighbor : curr.neighbors) {
                if (!map.containsKey(neighbor)) {
                    queue.offer(neighbor);
                    UndirectedGraphNode currCopy = new UndirectedGraphNode(neighbor.label);
                    map.put(neighbor, currCopy);
                }
            }
        }
    }
    for (UndirectedGraphNode originalNode : map.keySet()) {
        for (UndirectedGraphNode neighbor : originalNode.neighbors) {
            map.get(originalNode).neighbors.add(map.get(neighbor));
        }
    }
    return map.get(node);
}
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