54. Spiral Matrix

https://leetcode.com/problems/spiral-matrix/
Python

Time: O(m*n)
Space: O(m*n) # the visited hashmap
class Solution:
    def spiralOrder(self, matrix: List[List[int]]) -> List[int]:
        m = len(matrix)
        n = len(matrix[0])

        limit = m*n
        visited = set()
        result = []

        direction = 'right'
        x, y = 0, 0
        while len(result) < limit:
            result.append(matrix[y][x])
            visited.add((x, y))

            if direction == 'right':
                if x+1 < n and (x+1, y) not in visited:
                    x += 1
                else:
                    direction = 'down'
                    y += 1
            elif direction == 'down':
                if y+1 < m and (x, y+1) not in visited:
                    y += 1
                else:
                    direction = 'left'
                    x -= 1
            elif direction == 'left':
                if x-1 >= 0 and (x-1, y) not in visited:
                    x -= 1
                else:
                    direction = 'up'
                    y -= 1
            else:
                if y-1 >= 0 and (x, y-1) not in visited:
                    y -= 1
                else:
                    direction = 'right'
                    x += 1

        return result
Python​

Python
