918. Maximum Sum Circular Subarray

/*
 * @lc app=leetcode id=918 lang=cpp
 *
 * [918] Maximum Sum Circular Subarray
 *
 * https://leetcode.com/problems/maximum-sum-circular-subarray/description/
 *
 * algorithms
 * Medium (46.01%)
 * Likes:    6878
 * Dislikes: 320
 * Total Accepted:    319.7K
 * Total Submissions: 682K
 * Testcase Example:  '[1,-2,3,-2]'
 *
 * 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
 * 1 <= n <= 3 * 10^4
 * -3 * 10^4 <= nums[i] <= 3 * 10^4
 *
 *
 */

// @lc code=start
class Solution {
public:
    int maxSubarraySumCircular(vector<int>& nums) {
        int curMax = 0, curMin = 0;
        int maxSum = nums[0], minSum = nums[0];
        int totalSum = 0;

        for(int num : nums) {
            curMax = max(curMax + num, num);
            maxSum = max(maxSum, curMax);

            curMin = min(curMin + num, num);
            minSum = min(minSum, curMin);

            totalSum += num;
        }
        if(totalSum == minSum) {
            return maxSum;
        }
        return max(maxSum, totalSum - minSum);
    }
};
// @lc code=end

• T: $O(N)$
• S: $O(1)$