713. Subarray Product Less Than

双指针,滑动窗口
数组长度n
n = len(nums)
p记录乘积
p = 1
i为begin,窗口左端. j为end,窗口右端
i = 0 j = 0
total记录符合条件subarray个数
total = 0

while j < n:
            p *= nums[j]
            while i <= j and p >= k:
                p /= nums[i]
                i += 1
            total += j - i + 1
            j += 1

尽量扩展窗口

最后返回total
return total