Day2 . 59. 螺旋矩阵 II

题目链接：https://leetcode.cn/problems/spiral-matrix-ii/

核心思想:模拟

• 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

• 左闭右开

class Solution(object):
    def generateMatrix(self, n):
        nums = [[0]* n for _ in range(n)]
        startx,starty = 0,0

        loop,mid = n//2,n//2
        count = 1

        for offset in range(1,loop+1):
            for i in range(starty,n-offset):
                nums[startx][i] = count
                count += 1
            for i in range(startx,n-offset):
                nums[i][n-offset] = count
                count += 1
            for i in range(n-offset,starty,-1):
                nums[n-offset][i] = count
                count += 1
            for i in range(n-offset,startx,-1):
                nums[i][starty] = count
                count += 1
            startx += 1
            starty += 1
        
        if n % 2 != 0:
            nums[mid][mid] = count
        return nums

        

解析：

• nums = [[0]* n for _ in range(n)]：建二维列表（即n×n的矩阵）并初始化为全0

• startx,starty：起始(x,y)位置

• loop：转圈数 mid ：中心位置

• count：开始数

• startx += 1 starty += 1：每一圈完成后，起始位置就从(0,0)到(1,1)的下一个内圈