算法第二天

977.有序数组的平方 ，209.长度最小的子数组 ，59.螺旋矩阵II

977.有序数组的平方

class Solution:
    def sortedSquares(self, nums: List[int]) -> List[int]: # type: ignore
        # # 暴力解法
        # new_res = []
        # for num in nums:
        #     new_res.append(num**2)
        
        # return sorted(new_res)
    
        # 双指针解法
        # 原数组nums为非递减顺序，那么平方后最大的一定在首尾位置以此类推
        new_nums = []
        left, right = 0, len(nums) - 1
        while left <= right:
            if nums[left]**2 < nums[right]**2:
                new_nums.append(nums[right]**2)
                right -= 1
            else:
                new_nums.append(nums[left]**2)
                left += 1

        return new_nums[::-1]

209.长度最小的子数组

class Solution:
    def minSubArrayLen(self, target: int, nums: List[int]) -> int: # type: ignore
        l = len(nums)
        left = 0
        right = 0
        min_len = float('inf')
        cur_sum = 0

        while right < l:
            cur_sum += nums[right]

            while cur_sum >= target:
                min_len = min(min_len, right-left+1)
                cur_sum -= nums[left]
                left += 1
            
            right += 1
        
        return min_len if min_len != float('inf') else 0

59.螺旋矩阵II

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]: # type: ignore
        nums = [[0] * n for _ in range(n)]
        startx, starty = 0, 0               # 起始点
        loop, mid = n // 2, n // 2          # 迭代次数、n为奇数时，矩阵的中心点
        count = 1                           # 计数

        for offset in range(1, loop + 1) :      # 每循环一层偏移量加1，偏移量从1开始
            for i in range(starty, n - offset) :    # 从左至右，左闭右开
                nums[startx][i] = count
                count += 1
            for i in range(startx, n - offset) :    # 从上至下
                nums[i][n - offset] = count
                count += 1
            for i in range(n - offset, starty, -1) : # 从右至左
                nums[n - offset][i] = count
                count += 1
            for i in range(n - offset, startx, -1) : # 从下至上
                nums[i][starty] = count
                count += 1                
            startx += 1         # 更新起始点
            starty += 1

        if n % 2 != 0 :			# n为奇数时，填充中心点
            nums[mid][mid] = count 
            
        return nums