lc: 532 k diff pair
Brute force: T:O(nlogn) S:(n) -> Sorting + set
Time Optimal: T:(n) S:O(n) -> dictionary based
Space Optimal: T(nlogn) S:O(1) -> Sorting + 2 pointer
Time Optimal: T:(n) S:O(n) -> dictionary based
Space Optimal: T(nlogn) S:O(1) -> Sorting + 2 pointer