918. Maximum Sum Circular Subarray LeetCode Java 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

Solution

class Solution {
    public int maxSubarraySumCircular(int[] nums) {
    return maxsum(nums);
    }
        public static int maxsum(int[] arr) 
    {
        int linear_sum=kadens(arr);
        int totalsum=0;
        for(int i=0;i<arr.length;i++)
        {
            totalsum+=arr[i];
            arr[i]=arr[i]*-1;
        }
        int mid_sum=kadens(arr);
        int curr_sum=totalsum+mid_sum;
        if(curr_sum==0)
        {
            return linear_sum;
        }
        return Math.max(linear_sum,curr_sum);
        
    }
    public static int kadens(int[] arr) 
    {
        int ans=Integer.MIN_VALUE;
        int sum=0;
        for(int i=0;i<arr.length;i++)
        {
            sum=sum+arr[i];
            ans=Math.max(ans,sum);
            if(sum<0)
            {
                sum=0;
            }
        }
        return ans;
        
    }
}