Contains Duplicate

Contains Duplicate is a Easy Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Array/Matrix Manipulation Patterns pattern, in the Hashing - Previously Seen / Existence Check subpattern.

Problem statement

Given nums, determine whether any integer occurs at least twice in the array. Two occurrences count as a duplicate even if they are at different positions.

Return true if nums contains a repeated value. Return false if every value appears exactly once.

Example 1:

Input: nums = [8,3,5,8] Output: true Explanation: The value 8 appears at two positions, so the array contains a duplicate.

Example 2:

Input: nums = [-4,12,0,7] Output: false Explanation: All four values are different, so no duplicate exists.

Example 3:

Input: nums = [6,6] Output: true Explanation: Both elements have the same value, which is enough to make the result true.

Constraints:

- 1 <= nums.length <= 10^5 - -10^9 <= nums[i] <= 10^9 - nums contains only integers.

Topics and companies

Topics: Array, Hash Table.

How to practise Contains Duplicate on Thita.ai

Starter code is provided in C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(n) expected time and O(n) space.

Open Contains Duplicate in the code editor, or read the Contains Duplicate editorial for a worked solution with its approach and complexity analysis.

Where Contains Duplicate sits in the DSA pattern sheet

Problems related to Contains Duplicate

Other problems that use the same Hashing - Previously Seen / Existence Check and Array/Matrix Manipulation Patterns techniques:

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