问题描述

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.

问题分析

思路是滑动解决。
设置left、right两个指针，total记录下标在left到right之间的数字的和。起始left、right均置为0，向后移动right，直至total大于等于s；向后移动left，直至total<s，此时right-left+1为subarray的长度。交替移动right和left，直到right到达末尾。

AC代码

class Solution(object):
    def minSubArrayLen(self, s, nums):
        """
        :type s: int
        :type nums: List[int]
        :rtype: int
        """
        n = len(nums)
        if n == 0:
            return 0
        left = right = total = 0
        opt = n+1
        while right < n:
            while right < n and total < s:
                total += nums[right]
                right += 1
            if total < s:
                break
            while left < right and total >= s:
                total -= nums[left]
                left += 1
            if right - left + 1 < opt:
                opt = right - left + 1
        return opt if opt <= n else 0

Runtime: 52 ms, which beats 68.97% of Python submissions.