Contains Duplicate - Insight

Approach 1 (Brute Force): Compare every pair. Time: $O(n^2)$, Space: $O(1)$.

Approach 2 (Sorting): Sort then check adjacent elements. Time: $O(n \log n)$, Space: $O(1)$ or $O(n)$ depending on sort.

Approach 3 (Hash Set): Add elements to a set, check for duplicates. Time: $O(n)$, Space: $O(n)$. The hash set trades space for better time.