[5/10] 59. Spiral Matrix II

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        ret = [[-1 for x in range(n)] for x in range(n)]
        cur_val, cur_dir = 0, 0
        directions = [(0,1), (1,0), (0,-1), (-1,0)]
        y, x = 0, 0
        prev_y, prev_x = 0, 0
        while cur_val < n*n:
            while x >= 0 and x < n and y >= 0 and y < n and ret[y][x] == -1:
                cur_val += 1
                ret[y][x] = cur_val
                prev_y, prev_x = y, x
                y = prev_y + directions[cur_dir][0]
                x = prev_x + directions[cur_dir][1]
            cur_dir = (cur_dir +1) % 4
            y = prev_y + directions[cur_dir][0]
            x = prev_x + directions[cur_dir][1]
        return ret