Looping in a spiral

Question

A friend was in need of an algorithm that would let him loop through the elements of an NxM matrix (N and M are odd). I came up with a solution, but I wanted to see if my fe

Answer 1

This is based on your own solution, but we can be smarter about finding the corners. This makes it easier to see how you might skip over the areas outside if M and N are very different.

def spiral(X, Y):
    x = y = 0
    dx = 0
    dy = -1
    s=0
    ds=2
    for i in range(max(X, Y)**2):
            if abs(x) <= X and abs(y) <= Y/2:
                    print (x, y)
                    # DO STUFF...
            if i==s:
                    dx, dy = -dy, dx
                    s, ds = s+ds/2, ds+1
            x, y = x+dx, y+dy

and a generator based solution that is better than O(max(n,m)^2), It is O(nm+abs(n-m)^2) because it skips whole strips if they are not part of the solution.

def spiral(X,Y):
X = X+1>>1
Y = Y+1>>1
x = y = 0
d = side = 1
while x