程式碼隨想錄演算法訓練營Day2|209.長度最小的子陣列 59.螺旋矩陣

學習資料：https://programmercarl.com/陣列總結篇.html#陣列的經典題目

移動窗格，首尾指標根據條件變化
模擬行為，迴圈不變數（左閉右閉或左閉右開）整個過程保持一致

學習記錄：
209.長度最小的子陣列（用while使得尾指標遍歷全部；用while實現，當[首:尾]之和>目標值，才移動首指標；為了求最小長度，先設定最小長度為正無窮float('inf')）

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class Solution(object):
    def minSubArrayLen(self, target, nums):
        """
        :type target: int
        :type nums: List[int]
        :rtype: int
        """
        begin=0
        end=0
        sum=0
        min_len=float('inf')   #設定為無窮大，方便找到最小值
        while end < len(nums):
            sum += nums[end]
            while sum >= target:
                sum -= nums[begin]
                sub_l=end-begin+1
                min_len = min(sub_l, min_len)
                begin += 1
            end += 1
        if min_len != float('inf'):
            return min_len
        else:
            return 0

59.螺旋矩陣(邊界值很多，有初始橫縱指標、左閉右開需要從n剪掉的offset、從1開始計數的count；當奇數階矩陣，中間多出來的1項單獨設定；螺旋轉的圈數為n//2)

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class Solution(object):
    def generateMatrix(self, n):
        """
        :type n: int
        :rtype: List[List[int]]
        """
        start_x = 0
        start_y = 0
        nums = [[0]*n for _ in range(n)]
        cycle, mid = n//2, n//2
        offset=1
        count=1
        for c in range(cycle):
            for j in range(start_y, n-offset):
                nums[start_x][j]=count
                count += 1
            for i in range(start_x, n-offset):
                nums[i][n-offset]=count 
                count += 1
            for j in range(n-offset, start_y, -1):
                nums[n-offset][j]=count
                count += 1
            for i in range(n-offset, start_x, -1):
                nums[i][start_y] = count
                count += 1
            start_x += 1
            start_y += 1
            offset += 1
        if n%2 != 0:
            nums[mid][mid]=count
        return nums

PS:
螺旋矩陣好繞啊，被9個數字給繞麻了
今天陰天，好冷，終於要放假了