Contains Duplicate (LeetCode 217) | Full solution with HashSet explanation in python
Given an array of integers, determine if any value appears more than once. Return true if there are duplicates, false if all elements are unique. Uses a hash set for O(n) time complexity.
Example: nums = [1,2,3,1] → true (1 appears twice)
Pattern: Hash set tracking, array traversal
Difficulty: Easy