how to search elements in a 2d array using recursion

Question

I have a 2d char array and I'm trying to find a specific character using recursion.

public class Test {

char arry [][] = {{'1',' ','B'},
                  {'C','K','M'},
                  {'H','R','P'}
};

public Test(){
    recursion(0,0,arry[0][0]);

}
private void recursion(int row, int col, char c) {
    if(c==' '){
        System.out.print("Location: " + row + " " + col );
    }else
    {
        if(col+1<arry[0].length){
            recursion(row,col,c);
        }
                    //System.out.print(arry[0][1]);

    }

}
public static void main(String[] args) {

    new Test();
}

}

but this is giving me a stack overflow. how can I find an element in a 2d array using recursion.

Your method calls itself with exactly the same argument values. — JB Nizet
– JB Nizet, Commented Mar 16, 2014 at 8:47

aashnisshah · Accepted Answer · 2014-03-16 09:05:16Z

1

It looks like your if statement isn't being executed properly. You are checking to check if c == " ", though I think you meant it to check if array[row][col]==c. Also, it seems like you never actually increment the values of row and col, so the recursion continuously happens on itself. Since the recursion values never change, and the check can never be true, this will eventually lead to a stackoverflow.

Try something along these lines:

private void recursion(int row, int col, char c) {
    if(array[row][col]==c){
        System.out.print("Location: " + row + " " + col );
    } else {
        if(col+1<array[0].length){
            recursion(row,col+1,c);
        } else if(row + 1<array[1].length){
            recursion(row+1,0,c);
        } else {
            System.out.print("Does not exist");
            //System.out.print(arry[0][1]); 
        }
    }
}

edited Mar 16, 2014 at 9:05

answered Mar 16, 2014 at 8:52

aashnisshah

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Comments

Salah · Accepted Answer · 2014-03-16 08:49:07Z

0

You method is calling itself with same values all the time.

recursion(row,col,c);

Update your value then send it to the method again. so it could look for another element in your array

For example:

recursion(row,++col,c);

answered Mar 16, 2014 at 8:49

Salah

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Comments

Bhavesh Munot · Accepted Answer · 2014-03-16 08:55:25Z

0

private void recursion(int row, int col, char c) {
if(c==' '){
    System.out.print("Location: " + row + " " + col );
}else
{
    if(col+1<arry[0].length){
        recursion(row,col+1,c);
    }
    else
         recursion(row+1, 0, c)
                //System.out.print(arry[0][1]);

}

}

answered Mar 16, 2014 at 8:55

Bhavesh Munot

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Comments

Mr. Polywhirl · Accepted Answer · 2015-10-26 20:52:53Z

The easiest way to search for a value in a 2D-Array would be to start at (0, 0) and scan through the entire column before advancing to the next row. When a value matches what you are looking for, return that location.

Here is an example.

import java.util.Arrays;

public class Find2D {
    public static int[] search(char[][] arr, char ch, int row, int col) {
        if (arr[row][col] == ch) {
            return new int[] { row, col };
        } else {
            if (col + 1 < arr[0].length) {
                return search(arr, ch, row, col + 1);
            } else if (row + 1 < arr[1].length) {
                return search(arr, ch, row + 1, 0);
            }
        }
        return null;
    }

    public static int[] search(char[][] arr, char ch) {
        return search(arr, ch, 0, 0);
    }

    public static void printr(int[] result) {
        System.out.println("Location: " + Arrays.toString(result));
    }

    public static void main(String[] args) {
        char arr[][] = {
            { '1', ' ', 'B' },
            { 'C', 'K', 'M' },
            { 'H', 'R', 'P' }
        };

        printr(search(arr, arr[0][0])); // [0, 0]
        printr(search(arr, 'M'));       // [1, 2]
        printr(search(arr, 'x'));       // null
    }
}

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