209. Minimum Size Subarray Sum

https://leetcode.com/problems/minimum-size-subarray-sum/#/description

Given an array of n positive integers and a positive integer s, find the minimal length of a contiguous subarray of which the sum ? s. If there isn‘t one, return 0 instead.

For example, given the array [2,3,1,2,4,3] and s = 7,
the subarray [4,3] has the minimal length under the problem constraint.

Sol:

https://discuss.leetcode.com/topic/13759/python-3-different-ac-solutions

class Solution(object):
    def minSubArrayLen(self, s, nums):
        """
        :type s: int
        :type nums: List[int]
        :rtype: int
        """

        # two pointers
        if len(nums) == 0:
            return 0

        sum = 0
        i = 0
        # fast pointer j
        j = 0
        res = len(nums) + 1
        while sum < s:
            sum += nums[j]
            j += 1

            # to enter the while loop below, sum is greater than s, now let‘s use another pointer i(slow) pointer to find the intervals between i and j.  

            while sum >= s:
                # if i and j still have elements among them
                if  res > j - i:
                    res = j - i
                sum -= nums[i]
                i += 1

            if j == len(nums):
                break

        # if sum > s at the very beginning, then the program will not enter the first while loop. Thus 0 will be returned.
        if res > len(nums):
            return 0

        return res