Algo:

- Traverse the array taking each element “a” as the middle element.
- Maintain 2 ordered maps- “left” and “right”. “left” has all elements to the left of “a” and “right” has the right ones.
- Binary search “left” to get max element less than “a”. Similarly binary search “right” to get the max element greater than “a”. Return -inf if not possible.
- The two search result form a triplet with “a”. Compare this sum with maxSum;
- Return maxSum

Time : O(nlogn)

Space : O(n)