0059_Spiral-Matrix-ii【M】

• JY：矩阵的螺旋遍历
• 相似题：0054_Spiral-Matrix【M】
• 参考：0059_Spiral-Matrix-ii【M】 

1、基于 4 个边界指针

• 参考 0054_Spiral-Matrix【M】中的解法 2

class Solution:
    def generateMatrix(self, n: int) -> [[int]]:
        left, right, top, bottom = 0, n-1, 0, n-1
        # jy: 初始化矩阵框架, 初始值均为 0
        matrix = [[0 for _ in range(n)] for _ in range(n)]
        # jy: 计算待填充的数值范围 [num, max_num]
        num, max_num = 1, n * n
        # jy: 数值范围确定, 不会存在边界指针越界问题
        while num <= max_num:
            for i in range(left, right + 1): 
                matrix[top][i] = num
                num += 1
            top += 1

            for i in range(top, bottom + 1): 
                matrix[i][right] = num
                num += 1
            right -= 1

            for i in range(right, left - 1, -1):
                matrix[bottom][i] = num
                num += 1
            bottom -= 1

            for i in range(bottom, top - 1, -1):
                matrix[i][left] = num
                num += 1
            left += 1
        return matrix
        

n = 1
res = Solution().generateMatrix(n)
print(res)
"""
[[1]]
"""

2、改写解法 1

• 完全参照 0054_Spiral-Matrix【M】的解法 2

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        left, right, top, bottom = 0, n-1, 0, n-1
        matrix = [[0 for _ in range(n)] for _ in range(n)]
        num = 1
        # jy: 数值范围只确定了初始数值, 结束数值未定, 因此填充时可能存
        #     在边界指针越界问题
        while True:
            for i in range(left, right + 1):
                matrix[top][i] = num
                num += 1
            top += 1
            if top > bottom:
                break

            for i in range(top, bottom + 1):
                matrix[i][right] = num
                num += 1
            right -= 1
            if right < left:
                break

            for i in range(right, left - 1, -1):
                matrix[bottom][i] = num
                num += 1
            bottom -= 1
            if bottom < top:
                break

            for i in range(bottom, top - 1, -1):
                matrix[i][left] = num
                num += 1
            left += 1
            if left > right:
                break
        return matrix


n = 3
res = Solution().generateMatrix(n)
print(res)
"""
[[1, 2, 3],
 [8, 9, 4],
 [7, 6, 5]]
"""