27. Contains Duplicate - Duplicate Detection

You're building a validation system for an e-commerce cart or form submission. You need to check if a user has duplicate items in their cart or if there are duplicate IDs in a form submission.

Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

Examples

containsDuplicate([1,2,3,1]);     // true - 1 appears twice
containsDuplicate([1,2,3,4]);     // false - all distinct
containsDuplicate([1,1,1,3,3,4,3,2,4,2]); // true - multiple duplicates