59. Spiral Matrix II

Python

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        matrix = [[None]*n for i in range(n)]

        direction = 'right'
        x, y = 0, 0

        for i in range(1, n**2+1):            
            matrix[y][x] = i
            
            if direction == 'right':
                if x+1 < n and matrix[y][x+1] is None:
                    x += 1
                else:
                    direction = 'down'
                    y += 1
            elif direction == 'down':
                if y+1 < n and matrix[y+1][x] is None:
                    y += 1
                else:
                    direction = 'left'
                    x -= 1
            elif direction == 'left':
                if x-1 >= 0 and matrix[y][x-1] is None:
                    x -= 1
                else:
                    direction = 'up'
                    y -= 1
            else:
                # up
                if y-1 >= 0 and matrix[y-1][x] is None:
                    y -= 1
                else:
                    direction = 'right'
                    x += 1
        
        return matrix