lintcode-medium-Route Between Two Nodes in Graph

Given a directed graph, design an algorithm to find out whether there is a route between two nodes.

 

Example

Given graph:

A----->B----->C
 \     |
  \    |
   \   |
    \  v
     ->D----->E

for s = B and t = E, return true

for s = D and t = C, return false

 

/**
 * Definition for Directed graph.
 * class DirectedGraphNode {
 *     int label;
 *     ArrayList<DirectedGraphNode> neighbors;
 *     DirectedGraphNode(int x) {
 *         label = x;
 *         neighbors = new ArrayList<DirectedGraphNode>();
 *     }
 * };
 */
public class Solution {
   /**
     * @param graph: A list of Directed graph node
     * @param s: the starting Directed graph node
     * @param t: the terminal Directed graph node
     * @return: a boolean value
     */
    public boolean hasRoute(ArrayList<DirectedGraphNode> graph, DirectedGraphNode s, DirectedGraphNode t) {
        // write your code here
        
        Queue<DirectedGraphNode> queue = new LinkedList<DirectedGraphNode>();
        
        HashSet<DirectedGraphNode> set = new HashSet<DirectedGraphNode>();
        
        if(s == t)
            return true;
        
        queue.offer(s);
        set.add(s);
        
        while(!queue.isEmpty()){
            
            DirectedGraphNode temp = queue.poll();
            
            for(DirectedGraphNode node: temp.neighbors){
                if(node == t)
                    return true;
                if(!set.contains(node)){
                    queue.offer(node);
                    set.add(node);
                }
            }
            
        }
        
        return false;
    }
}