Leetcode - Maximum Sum Circular Subarray (Python)

May 2020 Leetcode Challenge
Leetcode - Maximum Sum Circular Subarray

[CongNguyen-ogiz]

Thanks so much. Literally the best explanation out there

[mahirislam]

this is so much better than neetcode's. thanks!

[xinli]

Very smart, but how am I supposed to figure this out? :(

[alienx]

Thanks a lot, I was struggling with this problem but now it became very clear.

[asishcodes]

Thanks a lot for the explanation. I code in C++ but your explanation was very good.

[codewithcarter]

Thanks so much! I always refer to your videos when stuck :)

Here's the code of my adaption of Tim's solution, I usually try to pause the video after his whiteboard explaination & re-attempt it.
Hope it helps someone!

```
# My adaptation of Tim's vid:
class Solution:
def maxSubarraySumCircular(self, nums):
N = len(nums)

# Case 1
maxSum = cur = -math.inf
for n in nums:
cur = max(cur + n, n)
maxSum = max(maxSum, cur)

# Case 2
runningSum, maxRunningSumRev = 0, -math.inf
maxRunningSumRevArr = [0] * N
for i, n in enumerate(nums[::-1]):
runningSum += n
maxRunningSumRev = max(maxRunningSumRev, runningSum)
maxRunningSumRevArr[N - i - 1] = maxRunningSumRev

runningSum, highest = 0, -math.inf
for i, n in enumerate(nums[:-1]):
runningSum += n
highest = max(highest, runningSum + maxRunningSumRevArr[i + 1])
return max(maxSum, highest)
```