Minesweeper Counting Mines not working

Question

So, im at the point of counting the number of nearby mines ASSUMING if the spot chosen had no mines and this is what I came up with:

public static int numNearbyMines( boolean [][]mines, int row, int col) {    

    int nearbyMines = 0;

    if (mines[row - 1][col] == true) {  nearbyMines += 1; }
    if (mines[row - 1][col - 1] == true) {  nearbyMines += 1; }
    if (mines[row -  1][col + 1] == true) {  nearbyMines += 1; }
    if (mines[row][col + 1] == true) {  nearbyMines += 1; }
    if (mines[row][col - 1] == true) {  nearbyMines += 1; }
    if (mines[row + 1][col] == true) {  nearbyMines += 1; }
    if (mines[row + 1][col - 1] == true) {  nearbyMines += 1; }
    if (mines[row + 1][col + 1] == true) {  nearbyMines += 1; }
    return nearbyMines;
}

However, I realized that this method would not work because if I chose a place such as a corner, it would be "reading" outside of the array, hence not working. How would I change this so that even if I picked a corner, it would only read inside the array?

You need to add a check if the address (like [row-1][col]) is a valid one (within bounds). This check is best done in a method. — c0der, Nov 02 '17 at 04:07

score 2 · Answer 1 · edited Nov 02 '17 at 04:16

2

My solution for this sort of issue is to make a function to read arrays safely. Example:

boolean readMines(int x, int y) {
    if(x >= 0 && x < mines.length && y >= 0 && y < mines[0].length) {
        return mines[x][y];
    }
    return false;
}

This checks to make sure it's safe to read at the indices you give it before reading, and assumes there's no mines in places that can't be read. It should work for what you need.

edited Nov 02 '17 at 04:16

c0der

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answered Nov 02 '17 at 02:52

Anonymous Noob

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Is this supposed to be a new method? or implemented within the method I put in above? – Brian Kang Nov 02 '17 at 02:54
@BrianKang That should be a new method somewhere in your code that you call instead of reading from the array directly. SIDENOTE: You don't need an "== true" on if statements with booleans inside of them. – Anonymous Noob Nov 02 '17 at 02:57
The idea is fine. The code is wrong. It will not compile. – c0der Nov 02 '17 at 04:05
@c0der What's the error? I can't see anything wrong with it, but maybe I'm just tired. – Anonymous Noob Nov 02 '17 at 04:07
Test it, compile it before posting. `return mines[x][y];` should be `return true;` . Also change the name of the method. – c0der Nov 02 '17 at 04:09
@c0der No it shouldn't, it's supposed to read the value at mines[x][y] IF there is a value to be read, otherwise returning false if there isn't. The purpose of the function isn't to figure out whether it's safe to read mines, it's to read mines safely. – Anonymous Noob Nov 02 '17 at 04:10
With return value set to `boolean`? – c0der Nov 02 '17 at 04:11
@c0der Yes, mines is a boolean array holding whether or not there's a mine located at the indices. – Anonymous Noob Nov 02 '17 at 04:13
OK. Sorry my mistake – c0der Nov 02 '17 at 04:15
@c0der It's fine, it's natural to skip over some code when you think you understand already. – Anonymous Noob Nov 02 '17 at 04:17

score 0 · Answer 2 · answered Nov 02 '17 at 04:13

You can add a check if the address (like [row-1][col]) is a valid one (within bounds). This check is best done in a method:

boolean isValid(int x, int y) {
    if(x >= 0 && x < mines.length && y >= 0 && y < mines[0].length) {
        return true;
    }
    return false;
}

Minesweeper Counting Mines not working

2 Answers2