918 - Maximum Sum Circular Subarray.

Medium

Given a circular integer array nums of length n, return the maximum possible sum of a non-empty subarray of nums.

A circular array means the end of the array connects to the beginning of the array. Formally, the next element of nums[i] is nums[(i + 1) % n] and the previous element of nums[i] is nums[(i - 1 + n) % n].

A subarray may only include each element of the fixed buffer nums at most once. Formally, for a subarray nums[i], nums[i + 1], ..., nums[j], there does not exist i <= k1, k2 <= j with k1 % n == k2 % n.

Example 1:

Input: nums = 1,-2,3,-2

Output: 3

Explanation: Subarray 3 has maximum sum 3.

Example 2:

Input: nums = 5,-3,5

Output: 10

Explanation: Subarray 5,5 has maximum sum 5 + 5 = 10.

Example 3:

Input: nums = -3,-2,-3

Output: -2

Explanation: Subarray -2 has maximum sum -2.

Constraints:

• n == nums.length

• <code>1 <= n <= 3 * 10⁴</code>

• <code>-3 * 10⁴<= numsi<= 3 * 10⁴</code>