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.
Visually, the graph looks like the following:

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

克隆問題常常用hashMap, 關鍵在於如何從一個點設置遍歷, 此處用list, 不斷遍歷, 不斷list. get(start++) ,再通過neighbour來獲取新的node.

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        // write your code here
        if (node == null) {
            return node;
        }
        
        HashMap<UndirectedGraphNode, UndirectedGraphNode> map = 
          new HashMap<UndirectedGraphNode, UndirectedGraphNode> ();
        ArrayList<UndirectedGraphNode> nodes = new ArrayList<UndirectedGraphNode>();
        
        //copy nodes
        nodes.add(node);
        map.put(node, new UndirectedGraphNode(node.label));
        int start = 0; 
        while (start < nodes.size()) {
            UndirectedGraphNode head = nodes.get(start++);
            for (UndirectedGraphNode n : head.neighbors) {
                if (!map.containsKey(n)) {
                    map.put(n, new  UndirectedGraphNode(n.label));
                    // 對nodes進行了add因此不能用foreach
                    nodes.add(n);
                }
            }
        }
        
        //copy neighbors
        for (UndirectedGraphNode i : nodes) {
            UndirectedGraphNode newNode = map.get(i);
            for (UndirectedGraphNode j : i.neighbors) {
                newNode.neighbors.add(map.get(j));
            }
        }
        return map.get(node);
}

}

133 Clone Graph