133. Clone Graph

Description

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:

graph

Solution

BFS

用Map保存clone graph nodes，Queue保存original graph nodes。

注意一定要提前判断non-null。。。

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList(); }
 * };
 */
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) {  // imporant! Otherwise NPE is invited
            return null;
        }
        
        Map labelToClone = new HashMap<>();
        labelToClone.put(node.label, new UndirectedGraphNode(node.label));
        Queue queue = new LinkedList<>();
        queue.offer(node);
        
        while (!queue.isEmpty()) {
            UndirectedGraphNode curr = queue.poll();
            
            for (UndirectedGraphNode neighbor : curr.neighbors) {
                if (!labelToClone.containsKey(neighbor.label)) {
                    labelToClone.put(neighbor.label
                                     , new UndirectedGraphNode(neighbor.label));
                    queue.offer(neighbor);
                }
                labelToClone.get(curr.label).neighbors
                    .add(labelToClone.get(neighbor.label));
            }
        }
             
        return labelToClone.get(node.label);
    }
}

DFS

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList(); }
 * };
 */
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        Map labelToClone = new HashMap<>();
        return cloneGraphRecur(node, labelToClone);
    }
    
    public UndirectedGraphNode cloneGraphRecur(
        UndirectedGraphNode node, Map labelToClone) {
        if (node == null) {
            return null;
        }
        
        if (labelToClone.containsKey(node.label)) {  // already handled
            return labelToClone.get(node.label);
        }
        
        UndirectedGraphNode clone = new UndirectedGraphNode(node.label);
        labelToClone.put(node.label, clone);
        
        for (UndirectedGraphNode neighbor : node.neighbors) {
            clone.neighbors.add(cloneGraphRecur(neighbor, labelToClone));
        }
        
        return clone;
    }
}