59.螺旋矩阵2.py

# 给定一个正整数 n，生成一个包含 1 到 n2 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 ]
# ]

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        l,r,t,b = 0,n-1,0,n-1
        mat = [[0 for _ in range(n)] for _ in range(n)]
        num, tar = 1, n * n
        while num <= tar:
            for i in range(l,r + 1): # left to right
                mat[t][i] = num
                num += 1
            t += 1
            for i in range(t, b + 1):  # top to bottom
                mat[i][r] = num
                num += 1
            r -= 1
            for i in range(r,l-1,-1):
                mat[b][i] = num
                num += 1
            b -= 1
            for i in range(b,t-1,-1):
                mat[i][l] = num
                num += 1
            l += 1
        return mat