918. Maximum Sum Circular Subarray | LeetCode Solution

 918. Maximum Sum Circular Subarray | LeetCode Solution

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

class Solution {

public:

    int maxSubarraySumCircular(vector<int>& nums) {

        int pre=nums[0];

        int post=nums[0];

        int total=accumulate(nums.begin(),nums.end(),0);

        int currmax=0,currmin=0;

        

        for(int i=0; i<nums.size(); i++){

            currmax=max(currmax+nums[i],nums[i]);

            currmin=min(currmin+nums[i],nums[i]);

            pre=max(pre,currmax);

            post=min(post,currmin);

        }

        if(total==post)return pre;

        return max(pre,total-post);

    }

};