Description:

Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

Example:

Input: 3

Output:
[
[ 1, 2, 3 ],
[ 8, 9, 4 ],
[ 7, 6, 5 ]
]

Solution:

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        
        result = []
        for i in range(n):
            result.append([0]*n)
            
        shift = {
            (0,1):((1,0),(0,1)),
            (1,0):((0,-1),(3,-1)),
            (0,-1):((-1,0),(1,-1)),
            (-1,0):((0,1),(2,1))
        } 
            
        wall = [-1,n,-1,n] # top bottom left right
        
        row,col = 0,0
        direction = (0,1)
        for i in range(1,n*n+1):
            # print(row,col,i)
            result[row][col] = i
            row += direction[0]
            col += direction[1]
            if row in wall[:2] or col in wall[2:]:
                row -= direction[0]
                col -= direction[1]
                direction,(i,j) = shift[direction]
                row += direction[0]
                col += direction[1]
                wall[i] += j
                
        return result

Performance:

• Runtime: 36 ms, faster than 86.61% of Python3 online submissions for Spiral Matrix II.
• Memory Usage: 13.2 MB, less than 30.65% of Python3 online submissions for Spiral Matrix II.