Solution: Find Symmetric Pairs in a List

Statement

Given a list of pairs, nums, find all the symmetric pairs from it.

A symmetric pair is defined as a pair [a, b] such that both [a, b] and [b, a] exist in the list.

• If no symmetric pair is found, return an empty list.

• Each symmetric pair should be returned once (you may return either [a, b] or [b, a]).

• The output can be in any order.

Constraints:

• $2 \leq$ nums.length $\leq10^3$ ...