leetcode 每日一题 59. 螺旋矩阵 II

模拟

思路:

参考54.螺旋矩阵

代码：

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        res = [[0]*n for _ in range(n)]
        dc = [1,0,-1,0]
        dr = [0,1,0,-1]
        seen = [[False]*n for _ in range(n)]
        r = c = di = 0
        for i in range(n*n):
            res[r][c] = i+1
            seen[r][c] = True
            cr, cc = r + dr[di], c + dc[di]
            if 0 <= cr < n and 0 <= cc < n and not seen[cr][cc]:
                r, c = cr, cc
            else:
                di = (di + 1) % 4
                r, c = r + dr[di], c + dc[di]
        return res

按层模拟

思路:

先建一个n*n二维数组，一层一层更新数组的值。

代码：

class Solution:
    def generateMatrix(self, n: int) -> [[int]]:
        l, r, t, b = 0, n - 1, 0, n - 1
        res = [[0]*n for _ in range(n)]
        num, tar = 1, n * n
        while num <= tar:
            for i in range(l, r + 1): 
                res[t][i] = num
                num += 1
            t += 1
            for i in range(t, b + 1):
                res[i][r] = num
                num += 1
            r -= 1
            for i in range(r, l - 1, -1): 
                res[b][i] = num
                num += 1
            b -= 1
            for i in range(b, t - 1, -1): 
                res[i][l] = num
                num += 1
            l += 1
        return res