Printing elements in nested array with recursion instead of loop

Question

I have been trying to print elements in

int[][]a= {{2,-36,98},{21,55},{2,5,4,7,6},{101}}

with the help of recursion instead of a loop. Now i have a piece of code with me but it prints extra unwanted elements.

public class RecursionDoubleLoop {
    void loop(int[][]a,int x,int y)
    {
        int n=a.length;
        if(x<n)
        {

            if(y<a[x].length)
            {

                System.out.println(a[x][y]+" ");

                y+=1;
                if(y<a[x].length)
                loop(a, x, y);
            }
            y=0;
            x+=1;
            /*if(x>=n)
            {
                System.exit(0);
            }*/
            if(x<n) {
            loop(a, x, y);}
        }
    }
    public static void main(String[] args) {
        RecursionDoubleLoop obj= new RecursionDoubleLoop();
        int[][]a= {{2,-36,98},{21,55},{2,5,4,7,6},{101}};
        obj.loop(a, 0, 0);
    }

}

Now the Expected Output is

2 -36 98 21 55 2 5 4 7 6 101

My output

2 -36 98 21 55 2 5 4 7 6 101 101 101 101 101 2 5 4 7 6 101 101 101 101 101 21 55 2 5 4 7 6 101 101 101 101 101 2 5 4 7 6 101 101 101 101 101 21 55 2 5 4 7 6 101 101 101 101 101 2 5 4 7 6 101 101 101 101 101

Tried debugging but ultimately had to uncomment the System.exit(0) function.

It will be very helpful if someone can point out the error.

Arvind Kumar Avinash · Accepted Answer · 2020-05-19 13:54:24Z

2

You're so close that it hurts to tell you the solution. All you need to do is simply return in the check for y < a[x].length. This is because the recursive call to loop is going to increase y until this is false and ultimately proceed to increase x. So close man.

if (y < a[x].length) {
    loop(a, x, y);
    return;
}

Output

edited May 19, 2020 at 13:54

Arvind Kumar Avinash

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answered May 19, 2020 at 13:38

Jason

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4 Comments

Regexes Over a year ago

Can u explain it a bit more coz I am a beginner and need some more knowledge regarding this.

Jason Over a year ago

Absolutely. Is there are particular part you're stumped on? Is it regarding the use of return?

Regexes Over a year ago

It is regarding the use of return and also why does my code didnt not work ? i mean i have used the if conditions correctly still :(

Jason Over a year ago

The code you provided didn't work because after each call to loop subsequently finished, the x was always being incremented and if x was less than n, it would loop again. By using return when looping through y, we don't increment x. By doing so, on the next call to loop, x will be incremented as intended. I hope this helps.

Silviu Burcea · Accepted Answer · 2020-05-19 13:51:15Z

You need to wrap your inner code in an else block when going to the next row. Also, a few checks are not needed there, since they will be caught by recursion.

void loop(int[][] a, int x, int y) {
    int n = a.length;
    if (x < n) {
        if (y < a[x].length) {
            System.out.print(a[x][y] + " ");
            loop(a, x, y + 1);
        } else {
            loop(a, x + 1, 0);
        }
    }
}

How I figured out? I printed "loop " + x + " " + y on the first line of the method to figure out what is wrong with your code. It was easy to see that your implementation was good but it was not stopping when increasing x.

If you want a compart implementation(basically, inverted if conditions), you can try this:

void loop(int[][] a, int x, int y) {
    if (x >= a.length) return;
    if (y >= a[x].length) {
        loop(a, x + 1, 0);
    } else {
        System.out.print(a[x][y] + " ");
        loop(a, x, y + 1);
    }
}

0xh3xa · Accepted Answer · 2020-05-19 14:02:14Z

0

Check if the x reaches the rows limit or y is greater than columns limit then return from the recursion.

, Check if the y reaches the columns limit then start new recursion to get the other arrays with x+1 and y 0 then return from the recursion.

, So the second condition will increase x and the inner recursion will increase y

    void loop(int[][] a, int x, int y) {
        if (x >= a.length || y > a[x].length)
            return;
        if (y == a[x].length) {
            System.out.println();
            loop(a, x + 1, 0);
            return;
        }

        System.out.print(a[x][y] + " ");
        loop(a, x, y + 1);
    }

, output

edited May 19, 2020 at 14:02

answered May 19, 2020 at 13:51

0xh3xa

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