visit.py

def spiral(m, n):
    """ Spiral matrix traversal (counterclockwise). """
    m -= 1
    dx, dy = 0, 1
    x, y = 0, -1
    while m >= 0 and n >= 0:
        for _ in range(m if dx else n):
            x += dx
            y += dy
            yield x, y
        m -= abs(dx)
        n -= abs(dy)
        dx, dy = dy, -dx


try:
    import pytest

    @pytest.mark.parametrize('m,n', [
        (1, 1),
        (3, 3),
        (4, 4),
        (4, 5),
        (5, 4),
        (9, 1),
        (1, 9),
    ])
    def test_spiral(m, n):
        res = list(spiral(m, n))
        assert len(res) == m * n
        assert len(set(res)) == len(res)
        for x, y in res:
            assert 0 <= x < m and 0 <= y < n
except ImportError:
    pass


if __name__ == '__main__':
    import sys
    assert len(sys.argv) > 1, 'Usage: visit.py MxN'
    d = map(int, sys.argv[1].split('x'))
    for p in spiral(*d):
        print('{}, {}'.format(*p))