pset 3 - game of fifteen - move tile

Question

I'm currently working on pset3 game of fifteen, and my move function is not working. Below is my code for move().

bool move(int tile)
{

for (int i = 0; i < d; i++)
{
    for (int j = 0; j < d; j++)
    {

        if (board[i][j] == tile)
        {
            if (board[i + 1][j] == 0)
            {
                int tmp = board[i][j];
                board[i][j] = board[i + 1][j];
                board[i + 1][j] = tmp;
                return true;
            }
            if (board[i][j + 1] == 0)
            {
                int tmp = board[i][j];
                board[i][j] = board[i][j + 1];
                board[i][j + 1] = tmp;
                return true;
            }
            if (board[i - 1][j] == 0)
            {
                int tmp = board[i][j];
                board[i][j] = board[i - 1][j];
                board[i - 1][j] = tmp;
                return true;
            }
            if (board[i][j - 1] == 0)
            {
                int tmp = board[i][j];
                board[i][j] = board[i][j - 1];
                board[i][j - 1] = tmp;
                return true;
            }
        }


    }
}

return false;
}

I have accounted for the '0' tile being above (board[i + 1][j]), below (board[i - 1][j]), left (board[i][j - 1]), and right (board[i][j + 1]). I used the following swapping method to swap the tiles.

int tmp = a;
int a = b;
int b = tmp;

However, when I run the program and input a tile to move, some (not all) of the numbers just turn to 0 (leaving the original 0 untouched as well) instead of actually swapping the tiles. Here is an excerpt:

7  0  0 
8  0  0 
5  4  3 

Any help would be appreciated. Thanks!

Answer 1

It looks like you didn't account for the corner cases where the blank is on the edge of the board. In other words, when you try to swap, i or j could go out of range, essentially swapping with something undefined and off the edge of the board. For instance, if the blank is in the bottom right corner and it tries to swap with i+1 or j+1, it will swap with undefined data.

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