Given a circular array C of integers represented by A, find the maximum possible sum of a non-empty subarray of C.
Here, a circular array means the end of the array connects to the beginning of the array.  (Formally, C[i] = A[i] when 0 <= i < A.length, and C[i+A.length] = C[i] when i >= 0.)
Also, a subarray may only include each element of the fixed buffer A at most once.  (Formally, for a subarray C[i], C[i+1], ..., C[j], there does not exist i <= k1, k2 <= j with k1 % A.length = k2 % A.length.)
Example 1:
Input: [1,-2,3,-2]
Output: 3
Explanation: Subarray [3] has maximum sum 3
Example 2:
Input: [5,-3,5]
Output: 10
Explanation: Subarray [5,5] has maximum sum 5 + 5 = 10
Example 3:
Input: [3,-1,2,-1]
Output: 4
Explanation: Subarray [2,-1,3] has maximum sum 2 + (-1) + 3 = 4
Example 4:
Input: [3,-2,2,-3]
Output: 3
Explanation: Subarray [3] and [3,-2,2] both have maximum sum 3
Example 5:
Input: [-2,-3,-1]
Output: -1
Explanation: Subarray [-1] has maximum sum -1
Note: 
-30000 <= A[i] <= 30000
1 <= A.length <= 30000
class Solution:
    def maxSubarraySumCircular(self, A: List[int]) -> int:
        def maxSum(gen):
            res = cur = -float('inf')
            for n in gen:
                cur = n + max(0, cur)
                res = max(res, cur)
            return res
        
        total = sum(A)
        res1 = maxSum(iter(A))
        res2 = total + maxSum(-A[i] for i in range(1, len(A))) # min sum of the unwated sub array
        res3 = total + maxSum(-A[i] for i in range(len(A)-1))
        return max(res1, res2, res3)
class Solution:
    def maxSubarraySumCircular(self, A: List[int]) -> int:
        def maxSum(gen):
            res = cur = -float('inf')
            for n in gen:
                cur = n + max(0, cur)
                res = max(res, cur)
            return res
        
        total = sum(A)
        res1 = maxSum(iter(A))
        res2 = total + maxSum(-A[i] for i in range(1, len(A))) # min sum of the unwated sub array
        res3 = total + maxSum(-A[i] for i in range(len(A)-1))
        return max(res1, res2, res3)