Tuesday, September 30, 2014

Leetcode: 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
         / \
         \_/


Code (Java):
/**
 * 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;
        }
        
        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        
        // create the new node
        UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);
        map.put(node, newNode);
        
        queue.offer(node);
        
        while (!queue.isEmpty()) {
            UndirectedGraphNode curr = queue.poll();
            List<UndirectedGraphNode> neighborNodes = curr.neighbors;
            
            for (UndirectedGraphNode neighbor : neighborNodes) {
                if (!map.containsKey(neighbor)) {
                    UndirectedGraphNode copy = new UndirectedGraphNode(neighbor.label);
                    map.put(neighbor, copy);
                    map.get(curr).neighbors.add(copy);
                    queue.offer(neighbor);
                } else {
                    map.get(curr).neighbors.add(map.get(neighbor));
                }
            }
        }
        
        return newNode;
    }
}




Update on 9/18/15:

/**
 * 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;
        }
        
        UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);
        
        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
        Queue<UndirectedGraphNode> queue = new LinkedList<>();
        
        queue.offer(node);
        map.put(node, newNode);
        
        while (!queue.isEmpty()) {
            UndirectedGraphNode curr = queue.poll();
            List<UndirectedGraphNode> neighbors = curr.neighbors;
            
            for (UndirectedGraphNode neighbor : neighbors) {
                if (!map.containsKey(neighbor)) {
                    UndirectedGraphNode newNeighbor = new UndirectedGraphNode(neighbor.label);
                    map.put(neighbor, newNeighbor);
                    map.get(curr).neighbors.add(newNeighbor);
                    queue.offer(neighbor);
                } else {
                    UndirectedGraphNode newNeighbor = map.get(neighbor);
                    map.get(curr).neighbors.add(newNeighbor);
                }
            }
        }
        
        return newNode;
    }
}











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