LeetCode 918: Maximum Sum Circular Subarray Solution

Master LeetCode problem 918 (Maximum Sum Circular Subarray), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

918. Maximum Sum Circular Subarray

Medium

Array Divide and Conquer Dynamic Programming Queue Monotonic Queue

Problem Explanation

Explanation

To solve this problem, we can use the Kadane's algorithm to find the maximum subarray sum. However, since the subarray can be circular, we need to consider two cases:

Maximum subarray sum without wrapping around.
Maximum subarray sum with wrapping around.

For the first case, we can use the regular Kadane's algorithm. For the second case, we can find the minimum subarray sum and then subtract it from the total sum to get the maximum subarray sum with wrapping around.

Finally, we compare the two cases and return the maximum value.

Time complexity: O(n)
Space complexity: O(1)

Solution Code

class Solution {
    public int maxSubarraySumCircular(int[] nums) {
        int totalSum = 0;
        int maxSum = nums[0], minSum = nums[0];
        int curMax = 0, curMin = 0;
        
        for (int num : nums) {
            curMax = Math.max(curMax + num, num);
            maxSum = Math.max(maxSum, curMax);
            
            curMin = Math.min(curMin + num, num);
            minSum = Math.min(minSum, curMin);
            
            totalSum += num;
        }
        
        if (maxSum > 0) {
            return Math.max(maxSum, totalSum - minSum);
        }
        
        return maxSum;
    }
}

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