# 918. Maximum Sum Circular Subarray (kadane-algo)

case1: noneCircularMaxSum

case2: circularMaxSum

![](https://4272748102-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-LekNH5IywF8mjBxFcnu%2Fuploads%2FT73uVybss6ON4Sji7oR0%2Fimage.png?alt=media\&token=2356fbd2-4be6-4b4e-abf4-d2a7eb920975)

corner case, all numbers are negative, minSum = total, so total - minsum = 0

result will be wrong : max(maxSum, 0) = 0, but we should return maxSum, 

so when total - minsum = 0 (circularMaxSum == 0), just return maxSum (noneCircularMaxSum)

![](https://4272748102-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-LekNH5IywF8mjBxFcnu%2Fuploads%2FloinLnBMH82ut4zoRNZo%2Fimage.png?alt=media\&token=55fb9ee8-cbaa-415b-a761-944902678207)

T: O(n)

S: O(1)

```java
class Solution {
    public int maxSubarraySumCircular(int[] nums) {
        int noneCircularMaxSum = kadane(nums);
        int total = 0;
        for (int i = 0; i < nums.length; i++) {
            total += nums[i];
            nums[i] = -nums[i];
        }
        int circularMaxSum = total + kadane(nums);
        if (circularMaxSum == 0) {
            return noneCircularMaxSum;
        }
        return Math.max(noneCircularMaxSum, circularMaxSum);
        
    }
    private int kadane(int[] nums) {
        int max = Integer.MIN_VALUE;
        int sum = 0;
        for (int num : nums) {
            sum += num;
            max = Math.max(max, sum);
            if (sum < 0) {
                sum = 0;
            }
        }
        return max;
    }
}

/*






  0. 1 2 3 4.  5
  5 -3 5 5 -3  5
0 5  2 7 12 9 14


  1,-2,3,-2 1,-2,3,-2
0 1 -1 2 0. 1.-1 2. 0


  -3 -2 -3 -3 -2 -3 
0 -3 -5 -8 -11 -13 -16

5  2 7 12 9 14


  [-2,-3,-1, -2, -3, -1]
0  -2 -5 -6  -8 -11. -12
*/
```