HasPath_usingDFS.java

/*
 *                      @Has path
 *    for given src & dest, tell if a path exists from src to dest.
 *      src=0, dest=5.
 */

import java.util.ArrayList;

public class HasPath_usingDFS {
    static class Edge {
        int src;
        int dest;
        int weight;

        Edge(int s, int d, int w) {
            this.src = s;
            this.dest = d;
            this.weight = w;
        }
    }

    public static void createGraph(ArrayList<Edge> graph[]) {
        for (int i = 0; i < graph.length; i++) {
            graph[i] = new ArrayList<>();
        }

        // 0 vertex
        graph[0].add(new Edge(0, 1, 1));
        graph[0].add(new Edge(0, 2, 1));

        // 1 vertex
        graph[1].add(new Edge(1, 0, 1));
        graph[1].add(new Edge(1, 3, 1));

        // 2 vertex
        graph[2].add(new Edge(2, 0, 1));
        graph[2].add(new Edge(2, 1, 1));

        // 3 vertex
        graph[3].add(new Edge(3, 1, 1));
        graph[3].add(new Edge(3, 4, 1));
        graph[3].add(new Edge(3, 5, 1));

        // 4 vertex
        graph[4].add(new Edge(4, 3, 1));
        graph[4].add(new Edge(4, 2, 1));
        graph[4].add(new Edge(4, 5, 1));

        // 5 vertex
        graph[5].add(new Edge(5, 4, 1));
        graph[5].add(new Edge(5, 3, 1));
        graph[5].add(new Edge(5, 6, 1));

        // 6 vertex
        graph[6].add(new Edge(6, 5, 1));
    }

    public static boolean hasPath(ArrayList<Edge>[] graph, int src, int dest, boolean vis[]) {

        if (src == dest) {
            return true;
        }
        vis[src] = true;
        for (int i = 0; i < graph[src].size(); i++) {
            Edge e = graph[src].get(i);
            if (!vis[e.dest] && hasPath(graph, e.dest, dest, vis)) {
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) {
        int v = 7;
        ArrayList<Edge>[] graph = new ArrayList[v];
        createGraph(graph);

        System.out.println(hasPath(graph, 0, 5, new boolean[v]));

    }
}

/*
 * Output:
 * true
 */