1
class Solution:
2
    def generateMatrix(self, n: int) -> List[List[int]]:
3
        if not n:
4
            return []
5
        matrix = [[0 for _ in range(n)] for _ in range(n)]
6
        left, right, top, bottom, num = 0, n - 1, 0, n - 1, 1
7
        while left <= right and top <= bottom:
8
            for i in range(left, right + 1):
9
                matrix[top][i] = num
10
                num += 1
11
            top += 1
12
            for i in range(top, bottom + 1):
13
                matrix[i][right] = num
14
                num += 1
15
            right -= 1
16
            if top <= bottom:
17
                for i in range(right, left - 1, -1):
18
                    matrix[bottom][i] = num
19
                    num += 1
20
                bottom -= 1
21
            if left <= right:
22
                for i in range(bottom, top - 1, -1):
23
                    matrix[i][left] = num
24
                    num += 1
25
                left += 1
26
        return matrix