18. Contains Duplicate

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

Input: An integer array nums.

Output: true if any duplicate exists, false if all elements are distinct.

Examples

Example 1

Input: [1,2,3,1]
Output: true
Explanation: Value 1 appears at index 0 and index 3. Duplicate found → return true.

Example 2

Input: [1,2,3,4]
Output: false
Explanation: All values 1,2,3,4 are distinct → return false.

Example 3

Input: [1,1,1,3,3,4,3,2,4,2]
Output: true
Explanation: 1,3,4,2 each appear multiple times → return true.