Route Between Directed Graph

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

Think

• Most typical Graph algorithm question!
• Try two ways: DFS, BFS.

Solution

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
     */

     // BFS
     public boolean hasRoute(ArrayList<DirectedGraphNode> graph, 
                            DirectedGraphNode s, DirectedGraphNode t) {

        if(s == t)
            return true;

        Queue<DirectedGraphNode> queue = new LinkedList<>();
        queue.offer(s);
        graph.remove(s);
        while(!queue.isEmpty()) {
            DirectedGraphNode cur = queue.remove();
               graph.remove(cur);
            for(DirectedGraphNode next : cur.neighbors) {
                if(!graph.contains(next))
                    continue;
                if(next == t)
                    return true;
                queue.offer(next);
            }
        }
        return false;
    }


    // DFS
    public boolean hasRoute(ArrayList<DirectedGraphNode> graph, 
                            DirectedGraphNode s, DirectedGraphNode t) {
        // write your code here
        if(s == t)
            return true;

        for(DirectedGraphNode next : s.neighbors) {
            if(hasRoute(graph, next, t))
                return true;
        }
        return false;
    }
}