// 918. Maximum Sum Circular Subarray #include "leetcode.h" /* * given: circular int array 'nums' of length 'n', return the max possible * sum of non-empty subarray of 'nums' * * a circular array means the end of the array connects to the beginning. * formally, the previous element of 'nums[i]' is 'nums[(i -/+ 1) % 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 */ class Solution { public: int maxSubarraySumCircular(vector &nums) { int sum = 0; for (int i : nums) sum += i; int s1 = helper(nums.begin(), nums.end()); for (int &i : nums) i *= -1; int s2 = sum + helper(nums.begin(), nums.end() - 1); int s3 = sum + helper(nums.begin() + 1, nums.end()); return max(s1, max(s2, s3)); } private: int helper(vector::iterator p, vector::iterator q) { int res = INT_MIN, n = 0; for (auto i = p; i != q; i++) { n += *i; res = max(res, n); if (n < 0) n = 0; } return res; } }; int main() { Solution obj; vector nums1 = {-2}, nums2 = {5, -3, 5}, nums3 = {-3, -2, -3}; cout << obj.maxSubarraySumCircular(nums1) << endl; // expect: 3 cout << obj.maxSubarraySumCircular(nums2) << endl; // expect: 10 cout << obj.maxSubarraySumCircular(nums3) << endl; // expect: -2 }