一、题目

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 * 104
-3 * 104 <= nums[i] <= 3 * 104

二、题解

class Solution {
public:int maxSubarraySumCircular(vector<int>& nums) {int n = nums.size();int all = nums[0],maxSum = nums[0],minSum = nums[0],maxPre = nums[0],minPre = nums[0];for(int i = 1;i < n;i++){all += nums[i];maxPre = max(nums[i],maxPre+nums[i]);maxSum = max(maxSum,maxPre);minPre = min(nums[i],minPre+nums[i]);minSum = min(minSum,minPre);}return all == minSum ? maxSum : max(maxSum,all - minSum);}
};