209. Minimum Size Subarray Sum 【M】【35】

Given an array of n positive integers and a positive integer s, find the minimal length of a 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.

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More practice:

If you have figured out the O(n) solution, try coding another solution of which the time complexity is O(n log n).

Credits:
Special thanks to @Freezen for adding this problem and creating all test cases.

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一个很有趣的双指针

从头到尾遍历，b每次增大一，然后观察a可以减少几个

class Solution(object):    def minSubArrayLen(self, s, nums):        if sum(nums) < s:            return 0        minn = 2 << 30           a,b = 0,0        total = nums[0]        res = 0        while total + nums[b] < s:            b += 1            total += nums[b]        res = b + 1        while b < len(nums):            while total - nums[a] >= s:                total -= nums[a]                a += 1            res = b - a + 1            minn = min(minn,res)            b += 1            try:                total += nums[b]            except:                break        return minn