Minimum Size Subarray Sum(追击指针）

Given an array ofnpositive integers and a positive integers, find the minimal length of acontiguoussubarray of which the sum ≥s. If there isn't one, return 0 instead.

Example:

Input:
s = 7, nums = [2,3,1,2,4,3]
Output:
 2

Explanation: 
the subarray 
[4,3]
 has the minimal length under the problem constraint.

分析

窗口类前向追击指针，注意这里sum < s要放在while里判断。防止j已经取过了头才退出。先判断再加J

class Solution:
    def minSubArrayLen(self, s, nums):
        """
        :type s: int
        :type nums: List[int]
        :rtype: int
        """
        if not nums:
            return 0
        n = len(nums)
        minLen =  n+1

        i = j = sum = 0
        for i in range(n):
            while j < n and sum < s:
                sum += nums[j]
                j+=1

            if sum >= s:
                minLen = min(minLen,j-i)
            sum-=nums[i]
        if minLen == n + 1:
            return 0
        return minLen