CODEWITHSUNDEEP
javaarraysdata-structuresdepth-first-search
jake
jake

Reputation: 95

java implementation of Depth First Search

the following code has no errors,but the output i am getting is not correct

import java.io.*;
class dfs
{
static void dfs(int a[][], int m[], int i, int n)
{
int j;
System.out.println("\t" + (i+1));
m[i] = 1;
for(j=0; j<n; j++)
    if(a[i][j]==1 && m[j]==0)
        dfs(a,m,j,n);
}  
public static void main(String args[]) throws IOException
{
int  n, i, j;
System.out.println("No. of vertices : ");
BufferedReader br= new BufferedReader (new InputStreamReader(System.in));
n =Integer.parseInt(br.readLine());
int m[]= new int[n];
int a[][] = new int[n][n];
for (i=0; i<n; i++)
{
    m[i] = 0;
}
System.out.println("\n\nEnter 1 if edge is present, 0 if not");
for (i=0; i<n; i++)
{
    System.out.println("\n");
    for (j=i; j<n; j++)
    {
        System.out.println("Edge between " + (i+1) + " and " +  (j+1)+ " : ");
        a[i][j] =Integer.parseInt(br.readLine());
        a[j][i]=a[i][j];
    }
    a[i][i] = 0;
}
System.out.println("\nOrder of accessed nodes : \n");
for (i=0; i<n; i++)
    if (m[i]==0)
        dfs(a,m,i,n);


}
}

Output Example

No of vertices : 8
edges
1 2
1 3
2 4
2 5
3 6
3 7
4 8
5 8
6 8
7 8

the DFS path should be : 1 2 4 8 5 3 6 7

the output i am getting is : 1 2 4 8 5 6 3 7

notice that the 6 th and 7 th terms are interchanged

can anyone tell me how to correct this.thanks for your help

Upvotes: 3

Views: 19215

Answers (4)

Mohammad
Mohammad

Reputation: 6138

You can try this implementation of DFS:

import java.util.ArrayList;
import java.util.List;

public class TreeTraverse {

    static class Node{
        Node(int data){
            this.data = data;
            this.left = null;
            this.right = null;
            this.visited = false;
        }
        int data;
        Node left;
        Node right;
        boolean visited;
    }

    public static void main(String[] args) {
        //The tree:
        //   1
        //  / \
        // 7   9
        // \  / \
        //  8 2 3

        Node node1 = new Node(1);
        Node node7 = new Node(7);
        Node node9 = new Node(9);
        Node node8 = new Node(8);
        Node node2 = new Node(2);
        Node node3 = new Node(3);
        node1.left = node7;
        node1.right = node9;
        node7.right = node8;
        node9.right = node3;
        node9.left = node2;
        System.out.println("DFS: ");
        depthFirstSearch(node1);

    }

    private static void depthFirstSearch(Node node){
        if(node.left == null && node.right == null){
            System.out.print(node.data+" ");
            node.visited = true;
        }else if(node.left == null || node.left.visited){
            depthFirstSearch(node.right);
            System.out.print(node.data+" ");
            node.visited = true;
        }else{
            depthFirstSearch(node.left);
            node.visited = true;
            System.out.print(node.data+" ");
            depthFirstSearch(node.right);

        }
    }

}

This is a recursive implementation of it. For more information please visit: https://github.com/m-vahidalizadeh/foundations/blob/master/src/algorithms/TreeTraverse.java. I hope it helps.

Upvotes: 0

Filipe Gon&#231;alves
Filipe Gon&#231;alves

Reputation: 21213

The output is correct. With your example, the recursion stops when i = 4 in dfs() (stops in vertex 5), and it winds back to vertex 8, where it came from (with i = 7). In this call, we have just returned from j = 4 (the one that had no more adjacent vertexes). The loop index is incremented (j++), and because vertex 8 is connected to vertex 6 (j = 5), the next recursive call will have i = 5, so you are visiting vertex 6. From vertex 6, the recursion goes to 3 and then 7, and then everything winds back.

Upvotes: 0

user902383
user902383

Reputation: 8640

i change implementation of your dfs, now it shopuld works, if you use names of variables, to make them more recognizable, you can get your help quicker

static void dfs(int adjacencyMatrix[][], int vertex, int[] visited) {

        System.out.println("visiting " + (vertex + 1) );


        for (int j = vertex + 1; j < adjacencyMatrix[vertex].length; j++)
            if (adjacencyMatrix[vertex][j] == 1 && visited[j] == 0) {
                visited[j] = 1;
                dfs(adjacencyMatrix, j, visited);
            }
    }

Upvotes: 4

ajb
ajb

Reputation: 31689

The output you're getting is correct for an undirected graph. The list of edges you provided includes (6,8), but a DFS can travel from 8 to 6 just as well as from 6 to 8 since it's undirected. If you want a directed graph, you'll have to make a couple changes in how the a array is set up.

Upvotes: 2

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