Find all pairs summing to X

Problem Given an array of UNIQUE non-negative integers and a target X, return all pairs of elements summing to X.

Input / Output

• Input: an int array of distinct values, and int X.
• Output: a list of pairs (each pair once; define the ordering).

Constraints

• n up to 10^5; O(n) expected.
• Values are distinct.

Example

• arr = [1,4,45,6,10,8], X = 16 -> [(6,10)].
• With X = 14 -> [(4,10), (6,8)].