How to implement dfs with recursion?

Question

I am trying to implement DFS with recursion using the following code,

public static void dfs(int i, int[][] mat, boolean [] visited){

  visited[i] = true;  // Mark node as "visited"

  System.out.print(i + "\t");

  for ( int j = 0; j < visited.length; j++ ){

     if ( mat[i][j] ==1  && !visited[j] ){

        dfs(j, mat, visited);       // Visit node
     }

  }
}

I have a matrix and an array to track visited nodes,

// adjacency matrix for uni-directional graph 
int [][] arr = {
                    // 1  2  3  4  5  6  7  8  9  10
                    {  0, 1, 1, 1, 0, 0, 0, 0, 0, 0}, // 1
                    {  0, 0, 0, 0, 0, 0, 1, 0, 0, 0}, // 2
                    {  0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, // 3 
                    {  0, 0, 0, 0, 1, 0, 0, 0, 0, 0}, // 4
                    {  0, 0, 0, 0, 0, 1, 0, 0, 0, 0}, // 5 
                    {  0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, // 6
                    {  0, 0, 0, 0, 0, 0, 0, 1, 1, 0}, // 7
                    {  0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, // 8 
                    {  0, 0, 0, 0, 0, 0, 0, 0, 0, 1}, // 9
                    {  0, 0, 0, 0, 0, 0, 0, 0, 0, 0}  // 10 
            };


   boolean [] visited = new boolean[10];

    for (int i =0; i< visited.length; ){

        visited[i++] = false;
    }

I make the call as follows:

dfs(1, arr, visited);

This is the return

// 1    6   7   8   9

which is wrong. He must return: [1 2 7 8 9 10 3 4 5 6]

The schedule is as follows:

How can I improve my code?

Answer 1

Your code is absolutely correct, just the call is incorrect. You call dfs on the 1st node, but root is on the 0th node.

So if you just replace

dfs(1, arr, visited);

from

dfs(0, arr, visited);

it will print the correct index order, which means that each element will be one less than your desired result, since the index of the Java array starts at 0.

, Java , boolean - false.

public class Dfs {
    public static void main(String[] args) {
        int[][] arr = {
                // 1 2 3 4 5 6 7 8 9 10
                { 0, 1, 1, 1, 0, 0, 0, 0, 0, 0 }, // 1
                { 0, 0, 0, 0, 0, 0, 1, 0, 0, 0 }, // 2
                { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, // 3
                { 0, 0, 0, 0, 1, 0, 0, 0, 0, 0 }, // 4
                { 0, 0, 0, 0, 0, 1, 0, 0, 0, 0 }, // 5
                { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, // 6
                { 0, 0, 0, 0, 0, 0, 0, 1, 1, 0 }, // 7
                { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, // 8
                { 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 }, // 9
                { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 } // 10
        };
        boolean [] visited = new boolean[10];

        dfs(0, arr, visited);

    }

    public static void dfs(int i, int[][] mat, boolean[] visited) {
        if(!visited[i]) {
            visited[i] = true; // Mark node as "visited"
            System.out.print( (i+1) + " ");

            for (int j = 0; j < mat[i].length; j++) {
                if (mat[i][j] == 1 && !visited[j]) {
                    dfs(j, mat, visited); // Visit node
                }
            }
        }
    }
}

1 2 7 8 9 10 3 4 5 6