918. Maximum Sum Circular Subarray

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:

1. -30000 <= A[i] <= 30000
2. 1 <= A.length <= 30000

# @lc code=start
using LeetCode

function max_subarray_sum_circular(nums)
    length(nums) < 1 && return 0
    csum = cur_max = maxn = cur_min = minn = nums[1]
    for i in 2:length(nums)
        csum += nums[i]
        cur_max = (cur_max > 0) ? cur_max + nums[i] : nums[i]
        maxn = max(maxn, cur_max)
        cur_min = (cur_min < 0) ? cur_min + nums[i] : nums[i]
        minn = min(minn, cur_min)
    end
    return maxn < 0 ? maxn : max(csum - minn, maxn)
end
# @lc code=end

max_subarray_sum_circular (generic function with 1 method)

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