Route Between Two Nodes in Graph

Source

• lintcode: 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

Java

/**
 * 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) {

        if (graph == null || s == null || t == null) return false;   

        Queue<DirectedGraphNode> q = new LinkedList<DirectedGraphNode>();
        Set<DirectedGraphNode> visited = new HashSet<DirectedGraphNode>();
        q.offer(s);

        while(!q.isEmpty()){
            DirectedGraphNode node = q.poll();
            visited.add(node);
            if(node==t) return true;
            for(DirectedGraphNode neighbor: node.neighbors){
                if(visited.contains(neighbor)) continue;
                q.offer(neighbor);
            }
        }
        return false;
    }
}