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.

Requirements

1. Basic Functionality

• Check if array contains any duplicates
• Return true if duplicates found, false otherwise
• Handle empty array (return false)
• Handle single element (return false)

Example Usage

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

Real-World Context

This problem models real validation scenarios:

• Cart validation: Check for duplicate items in shopping cart
• Form validation: Detect duplicate IDs or values
• Data cleaning: Identify duplicate entries in datasets
• ID validation: Ensure unique IDs in system