[leetcode] 209. Minimum Size Subarray Sum @ python

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于 2019-03-26 16:17:08 发布

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本文链接：https://blog.youkuaiyun.com/danspace1/article/details/88823246

本文介绍了一个算法问题：寻找满足一定条件的最小子数组长度。利用双指针法，通过不断移动左右指针来找到符合条件的最短子数组，并给出了解决方案的Python代码实现。

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原题

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.

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

解法

双指针法, 先遍历nums, 右指针移到使子序列的和>= s, 然后向右移动左指针, 使得subarray长度最短且和能>= s.

代码

class Solution(object):
    def minSubArrayLen(self, s, nums):
        """
        :type s: int
        :type nums: List[int]
        :rtype: int
        """
        total = left = 0
        res = len(nums)+1
        
        for right, n in enumerate(nums):
            total += n
            while total >= s:
                # update the res
                res = min(res, right-left+1)
                total -= nums[left]
                left += 1
        return res if res <= len(nums) else 0