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Counting Adjacent -1s In A 2d Array For A Given Row/column Without Checking Positions Out Of Bounds

- 1 answer

Need help figuring out a different way to write count(), it's something that will add to my code here:

public class Grid
{
    private int [][] array;
    private int max;

    public Grid(int max)
    {
        array = new int[10][10];
        this.max = max;
        setRandom();

    }

    public void setRandom()
    {
        int i = 0;
        while(i < max)
        {
            int r = (int)(Math.random() * 9) + 0;
            int c = (int)(Math.random() * 9) + 0;
            if(array[r][c] != -1)
                {
                    array[r][c] = -1;
                    i++;
                }
        }
    }
    
    public void print()
    {
        for(int r = 0; r < array.length; r++)
        {
            for(int c = 0; c < array[r].length; c++)
            {
                System.out.print(array[r][c] + " ");
            }
                System.out.println();
        }
    }

    public int count(int row, int col)
    {
    // method here
    }
        
    public static void main(String[] args)
    {
        Grid a = new Grid(20);
        a.count(5, 5);
        a.print();
    }
}

I want count() to return the number of -1s found in the 2d array surrounding the input position, and it also must not check a position "outside the bounds" (more specifically, the positions that aren't adjacent for a given row/column). Essentially it's like Minesweeper in a sense: let's say I pass in count(5, 5) (5 being the row and column respectively), it will check all adjacent positions surrounding (5, 5).

In this case, the highlighted blue is the position being checked and the yellow are adjacent positions. The white area is out of bounds and won't be checked. The position (5, 5) gets a value of 3 since there are 3 -1's surrounding the position. Visual here: https://imgur.com/a/0KCZdne

I came up with this code:

    public int count(int row, int col)
        {
            int value = 0;
            for(int r = -1; r < 2; r++)
            {
                for(int c = -1; c < 2; c++)
                {
                    if(c == 0 & r == 0)
                        continue;
                    if(array[row + r][col + c] == -1)
                    {
                        value++;
                    }
                }
            }
            return value;
        }

but when I pass in a.count(4, 7) in main(), nothing happens to the grid and it stays the same. I also want to find a different way to go about this without using continue This is the output:

0 0 -1 -1 0 -1 0 0 0 0 
-1 0 0 -1 -1 0 -1 0 0 0 
0 0 0 0 0 0 0 0 -1 0 
0 0 0 0 0 0 0 0 0 0 
-1 0 -1 0 0 0 0 -1 -1 0 
0 0 -1 -1 0 0 0 0 0 0 
0 0 -1 0 -1 0 0 0 -1 0 
0 0 -1 0 0 0 0 -1 0 0 
0 0 -1 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 0 0 

and I want my expected output to look something like this (if I passed in a.count(4, 7) - 4 being the row, 7 being the column)

0 0 -1 -1 0 -1 0 0 0 0 
-1 0 0 -1 -1 0 -1 0 0 0 
0 0 0 0 0 0 0 0 -1 0 
0 0 0 0 0 0 0 0 0 0 
-1 0 -1 0 0 0 0 -1 -1 0 
0 0 -1 -1 0 0 0 0 0 0 
0 0 -1 0 -1 0 0 0 -1 0 
0 0 -1 **4** 0 0 0 -1 0 0 
0 0 -1 0 0 0 0 0 0 0 
0 0 0 0 0 0 0 0 0 0 

(the 4 is the value in the position I passed in - since there are 4 -1s surrounding it, (3, 7) has a value of 4)

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Answer

You should check both the indices of row and column that you are trying to access is valid or not Just add a check to prevent ArrayIndexOutOfBoundsException.

public int count(int row, int col) {
        int value = 0;
        for(int r = -1; r < 2; r++) {
            for(int c = -1; c < 2; c++) {
                if(c == 0 & r == 0)
                        continue;
                int newR = row + r;
                int newC = col + c;

                if(newR < 0 || newR >= array.length || newC < 0 || newC >= array[0].length)
                    continue;
                
                if(array[newR][newC] == -1)
                    value++;
            }
        }
        return value;
    }

This is what I could come up with to avoid continue

     public int count(int row, int col) {
        int value = 0;
        value += isValidIndex(row - 1, col - 1)? array[row - 1][col - 1]: 0;
        value += isValidIndex(row - 1, col)? array[row - 1][col]: 0;
        value += isValidIndex(row - 1, col + 1)? array[row - 1][col + 1]: 0;
        value += isValidIndex(row, col - 1)? array[row][col - 1]: 0;
        value += isValidIndex(row, col + 1)? array[row][col + 1]: 0;
        value += isValidIndex(row + 1, col - 1)? array[row + 1][col - 1]: 0;
        value += isValidIndex(row + 1, col)? array[row + 1][col]: 0;
        value += isValidIndex(row + 1, col + 1)? array[row + 1][col + 1]: 0;
        return -value;
    }

    public boolean isValidIndex(int row, int col) {
        return !(row < 0 || col < 0 || row >= array.length || col >= array[0].length);
    }
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source: stackoverflow.com
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