PSET3 : fifteen: how to identify board edges in move function?

Question

Hi I am working on pset3 : fifteen and trying to implement move function. I'm not quite sure how to identify board edges and deal with this. My swap is also not working as the tile I want to move seems to override the blank "0" tile. Please see code below and I appreciate any suggestions on what to work on / why this isn't working...

bool move(int tile)
{
int temp;

for (int row = 0; row < d; row++){
    for (int col = 0; col < d; col++){
        if (board[row][col] == 0){
        if (board[row][col-1] == tile || board[row][col+1] == tile || board[row+1][col]==tile || board[row-1][col]==tile) {
            // legal move is permitted
             temp = board[row][col];
             board[row][col] = tile;
             tile = temp;
             return true;

        }
        }
    }
}


return false;
}

Answer 1

1. In the interest of efficiency, you might want to store the position of blank tile so you don't need to search the board for it each time you call move().
2. You need to check for the borders of your board through if statements first to determine if your move is legal before doing anything. In your above code, if col=d-1, for example, and you are trying to evaluate board[row][col+1], you will seg fault since col+1=d, but col only runs from 0 to d-1.

Answer 2

If you know the position of the blank tile (blankrow, blankcol) and the position of the user-entered tile (tilerow, tilecol) and you are confident that neither one of these tiles is off the board or out of bounds, then you do not need to add any logic to test the board edges.

A move will be valid if the user-entered tile is adjacent to the blank tile, which can be expressed in a single compound Boolean expression. In pseudocode:

if ((tilerow equals blankrow) and (tilecol equals blankcol plus or minus one)) OR ((tilecol equals blankcol) and (tilerow equals blankcol plus or minus one))

Also, the fact that the blank tile is always 0 should allow you to swap the two values in an unusually efficient manner!

Hope this helps!

NOTE: @ronga is right -- you do need to check the array bounds with your code as it currently stands. My point is just that there's a better way, and you could scrap the dangerous part of your code and use my method instead.