918. Maximum Sum Circular Subarray (kadane-algo)

case1: noneCircularMaxSum

case2: circularMaxSum

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)

T: O(n)

S: O(1)

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
*/