LeetCode 59. Spiral Matrix II

给定一个正整数 n，生成一个包含 1 到 n^2 所有元素，且元素按顺时针顺序螺旋排列的正方形矩阵。

示例:

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

模拟顺时针画矩阵的过程:

• 填充上行从左到右
• 填充右列从上到下
• 填充下行从右到左
• 填充左列从下到上

Python写法：

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        if not n:
            return []
        res = [[0 for _ in range(n)] for _ in range(n)]
        left, right, top, down, num = 0, n-1, 0, n-1, 1
        while left <= right and top <= down:
            for i in range(left, right+1):
                res[top][i] = num
                num += 1
            top += 1
            for i in range(top, down+1):
                res[i][right] = num
                num += 1
            right -= 1
            for i in range(right, left-1, -1):
                res[down][i] = num
                num += 1
            down -= 1
            for i in range(down, top-1, -1):
                res[i][left] = num
                num += 1
            left += 1
        return res

注意二维数组创建方法以及四个方向的变量变化。