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.

click to show more practice.

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