Java Iterating Through 2D-Array

Question

I have a 2D array in Java like so:

int 2d_arr[5][5];

Take, for example, the board that looks like this:

1 1 1 1 1
0 1 1 1 1
1 1 2 1 0
0 1 1 1 1
0 0 1 1 1

Starting from the 2 in the 3rd row, I want to be able to move in every direction (Up, down, left, right, and diagonals). In code, how do I traverse the array in every direction till I find a 0?

My theoretical idea would be to iterate in every direction sequentially. For example, start by going up, so I would check all the values on the line above 2

1
1
2

Since I didn't find any zeros, check the top right diagonal

   1
  1
 2

Still no 0s, so go onto the right. As soon as I find my first 0, break.

Attempt: I actually know how to do to this with a bunch of if and for loops, but I am looking for a way to edit that code to a simpler and easier to read version

But I'm new to java so I don't know the best way to go about this. Any ideas?

Answer 1

A TwoD Iterator would obviously be a good start. I expect you could do the rest yourself without much effort.

Finding the first zero in your scenario would involve iterating through each Direction and iterating across the board in that direction until the iteration ends or you find your zero.

Doing a spiral search would involve starting an iterator in each direction and doing a step and check on each one in turn until one returns a point where a zero can be found.

public class TwoDIteratorTest {

    // An ubiquitous Point class
    static class Point {
        final int x;
        final int y;

        public Point(int x, int y) {
            this.x = x;
            this.y = y;
        }

        @Override
        public String toString() {
            return "{" + x + "," + y + "}";
        }
    }

    // All possible directions.
    enum Direction {
        North(0, 1),
        NorthEast(1, 1),
        East(1, 0),
        SouthEast(1, -1),
        South(0, -1),
        SouthWest(-1, -1),
        West(-1, 0),
        NorthWest(-1, 1);
        private final int dx;
        private final int dy;

        Direction(int dx, int dy) {
            this.dx = dx;
            this.dy = dy;
        }

        // Step that way
        public Point step(Point p) {
            return new Point(p.x + dx, p.y + dy);
        }
    }

    static class TwoDIterator implements Iterable<Point> {
        // Where we are now
        Point i;
        // Direction to move in.
        private final Direction step;
        // Limits.
        private final Point min;
        private final Point max;
        // Next position to go to.
        Point next = null;

        // Normal constructor.
        public TwoDIterator(Point start, Direction step, Point min, Point max) {
            i = next = start;
            this.step = step;
            this.min = min;
            this.max = max;
        }

        // Some simplified constructors
        public TwoDIterator(int x, int y, Direction step, Point min, Point max) {
            this(new Point(x, y), step, min, max);
        }

        public TwoDIterator(int x, int y, Direction step, int minx, int miny, int maxx, int maxy) {
            this(new Point(x, y), step, new Point(minx, miny), new Point(maxx, maxy));
        }

        // The iterator.
        @Override
        public Iterator<Point> iterator() {
            return new Iterator<Point>() {
                // hasNext calculates next if necessary and checks it against the stabliched limits.
                @Override
                public boolean hasNext() {
                    if (next == null) {
                        // Step one.
                        next = step.step(i);
                        // Stop at limits.
                        if (next.x < min.x
                                || next.x > max.x
                                || next.y < min.y || next.y > max.y) {
                            next = null;
                        }
                    }
                    return next != null;
                }

                @Override
                public Point next() {
                    if (hasNext()) {
                        // Make our move.
                        i = next;
                        next = null;
                        return i;
                    }
                    return null;
                }

                @Override
                public void remove() {
                    throw new UnsupportedOperationException("Not supported.");
                }
            };
        }
    }

    public void test() {
        // Test all directions.
        for (Direction d : Direction.values()) {
            System.out.print(d + " - ");
            for (Point p : new TwoDIterator(0, 0, d, -5, -5, 5, 5)) {
                System.out.print(p + ",");
            }
            System.out.println();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new TwoDIteratorTest().test();
    }
}