Question

“Write a method in Java that returns true if there are k adjacent occurrences of a symbol in the same row, column, or diagonal of a checkered board (two-dimensional array), where k is the number of symbols inline desired.”

How can I do this? I have a rough idea of how to check rows and columns (very rough; no code, just thoughts) but I’m at a loss for checking the diagonal.

Edit: one other situation I’m thinking about: how can I check arbitrary positions? Right now, I’m only considering occurrences starting at (0,0), but what if there’s a string of 3 from, say, (2,3) to (2,6)? How could I keep track of multiple occurrences?

EDIT: Detecting the left diagonal (rough code for a question I posted in the comments below):

LeftDiagonal(x, symbol) {
    noOfOccurence = 0;

    for (currentX = (size - 1); currentX >= x; currentX--) {
        if (board[currentX][currentX] == symbol) {
            noOfOccurence++;
        } else {
            break;
        }
    }

    return (noOfOccurence >= k);
}

Answer 1

The simplest (though not the most efficient as it may backtrack) solution that comes to mind is to write a recursive function, like the following psuedocode

 FindAdjacent(x, y)
       if (matrix[x-1][y-1] == matrix[x][y])
            return 1 + FindAdjacent(x-1,y-1);
       .. Repeat for all 7 other adjacent locations (-1, +0) (+0, -1) (+1, -1) (-1, +1) (+1, +1) (+1, 0) (0, +1)
       else return 1;

This routine would, given a coordinate x,y, return the of symbols around it in a ‘blob’.
Note: This also means grouping of symbols such as 3 in a row, with 1 next to it in a column below.

If you were to call this once for every location in the matrix and see if the returned value once all recursive levels return is >= k, that might solve your problem. Remember to do bounds checking so you do not check matrix[-1][-1] or anything.