Pair Sum Problem Statement

Given an integer array ARR of size N and an integer S, your goal is to return a list of all pairs of elements such that the sum of elements of each pair equals S.

Example:

Input:

N = 5, S = 7
ARR = [1, 2, 3, 4, 5]

Output:

[2, 5]
[3, 4]

Explanation:

The pairs (2, 5) and (3, 4) are the pairs whose sums are equal to 7, sorted according to the given rules.

Constraints:

• 1 <= N <= 10^4
• -10^5 <= ARR[i] <= 10^5
• -2 * 10^5 <= S <= 2 * 10^5
• Time Limit: 1 sec

Note:

Each pair should be sorted such that the first value is less than or equal to the second value, and the list of pairs should be sorted in non-decreasing order based on the first value. In case two pairs have the same first value, the pair with a smaller second value should appear first.