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 #.

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
         / \
         \_/

1 map node to new node.

2 connection new nodes neighbors by getting old node's.

/**
 * 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) {
        if(node == null) return null;
        List<UndirectedGraphNode> nodes = new ArrayList<>();
        Map<UndirectedGraphNode,UndirectedGraphNode> map = new HashMap<>();

        nodes.add(node);
        map.put(node, new UndirectedGraphNode(node.label));

        int start =0;
        while(start < nodes.size()){
            UndirectedGraphNode n = nodes.get(start++);
            for(UndirectedGraphNode nn : n.neighbors){
                if(!map.containsKey(nn)){
                    map.put(nn, new UndirectedGraphNode(nn.label));
                    nodes.add(nn);
                }
            }
        }

        for(UndirectedGraphNode n : nodes){
            for(UndirectedGraphNode nn : n.neighbors){
                map.get(n).neighbors.add(map.get(nn));
            }
        }

        return map.get(node);

    }
}

The following solution failed cause this test case:

Input:{0,1,5#1,2,5#2,3#3,4,4#4,5,5#5}

Output:{0,1,5#1,2,5#2,3#3,4,4#4,5,5,5,5#5}

Expected:{0,1,5#1,2,5#2,3#3,4,4#4,5,5#5}

/**
 * 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) {

        if(node == null ) return node;
        // node < - > copy
        Map<UndirectedGraphNode,UndirectedGraphNode> map = new HashMap<>();   
        List<UndirectedGraphNode> list = new ArrayList<>();
        list.add(node);

        int k= 0;
        while(k < list.size()){
            UndirectedGraphNode cur = list.get(k++);
            UndirectedGraphNode copy = new UndirectedGraphNode(cur.label);
            map.put(cur, copy);
            Set<UndirectedGraphNode> keys = map.keySet();
            for(UndirectedGraphNode n : cur.neighbors){
                // if the neighbors is like 4,4,,4. then you add all the same instance into the list, multiple times.
                // But how possible ?
                if(!keys.contains(n)){
                    list.add(n);
                }
            }
        }

        for(UndirectedGraphNode n : list){
            for(UndirectedGraphNode nn : n.neighbors){
                map.get(n).neighbors.add(map.get(nn));
            }
        }   

        return map.get(node);
    }
}