leetcode [54] 螺旋矩阵

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给定一个包含 m x n 个元素的矩阵（m 行, n 列），请按照顺时针螺旋顺序，返回矩阵中的所有元素。

示例 1:

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

示例 2:

输入:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
输出: [1,2,3,4,8,12,11,10,9,5,6,7]

class Solution:
    def spiralOrder(self, matrix: List[List[int]]) -> List[int]:
        if len(matrix) == 0 or len(matrix[0]) == 0:
            return []
        ans = []
        left, right, up, down = 0, len(matrix[0]), 0, len(matrix)
        while left < right and up < down:
            for i in range(left, right):
                ans.append(matrix[up][i])
            up += 1
            for i in range(up, down):
                ans.append(matrix[i][right - 1])
            right -= 1
            if up < down:
                for i in range(right - 1, left - 1, -1):
                    ans.append(matrix[down - 1][i])
            down -= 1
            if left < right:
                for i in range(down - 1, up - 1, -1):
                    ans.append(matrix[i][left])
            left += 1
        return ans