spiral_traversal.py

class Solution:
    def spiral_print(self, matrix):
        seen = set()
        action_seq = [(0, +1), (+1, 0), (0, -1), (-1, 0)]
        act = 0
        curr = (0, 0)
        seen.add(curr)

        res = []
        res.append(matrix[curr[0]][curr[1]])

        changes = 0

        while True:

            if changes > 1:
                # finished
                return res

            """ becareful of tuple + tuple, that is (tuple, tuple)
            """
            next_move = (curr[0] + action_seq[act][0], curr[1] + action_seq[act][1]) 

            if 0 <= next_move[0] < len(matrix) and 0 <= next_move[1] < len(matrix[1]) and next_move not in seen:
                seen.add(next_move)
                curr = next_move
                changes = 0
                res.append(matrix[curr[0]][curr[1]])
            else:
                act +=1 
                changes +=1

            if act == len(action_seq):
                act = 0
            

grid = [[1,  2,  3,  4,  5],
        [6,  7,  8,  9,  10],
        [11, 12, 13, 14, 15],
        [16, 17, 18, 19, 20]]

print(Solution().spiral_print(grid))
# 1 2 3 4 5 10 15 20 19 18 17 16 11 6 7 8 9 14 13 12