[LeetCode]Maximum Subarray

public class Solution {
    public int maxSubArray(int[] nums) {
        return helper(nums, 0, nums.length - 1);
    }
    public int helper(int[] nums, int left, int right) {
        if (left > right) {
            return 0;
        }
        if (left == right) {
            return nums[left];
        }
        if (right - left == 1) {
            return Math.max(Math.max(nums[left], nums[left] + nums[right]), nums[right]);
        }
        int mid = left + (right - left) / 2;
        int mid_max = mid_max(nums, left, right);
        int left_max = helper(nums, left, mid - 1);
        int right_max = helper(nums, mid + 1, right);
        return Math.max(Math.max(mid_max, left_max), right_max);
    }
    public int mid_max(int[] nums, int left, int right) {
        int mid = (left + right) / 2;
        int left_max = Integer.MIN_VALUE;
        int right_max = Integer.MIN_VALUE;
        int l = 0;
        int r = 0;
        for (int i = mid - 1; i >= left; i --) {
            l += nums[i];
            left_max = Math.max(l, left_max);
        }
        for (int i = mid + 1; i <= right; i++) {
            r += nums[i];
            right_max = Math.max(r, right_max);
        }
        int[] arr = new int[]{left_max + right_max + nums[mid], nums[mid], nums[mid] + left_max, nums[mid] + right_max};
        Arrays.sort(arr);
        return arr[3];
    }
}