Remove Elements from Sorted Array
Given a sorted integer array nums, remove all duplicate elements in-place such that each unique element appears only once.
The relative order of the elements should be maintained.
Return the number of unique elements.
The first k elements of the array should contain the unique elements after removing duplicates.
Example 1
Input
5 1 1 2 2 3
Output
3 1 2 3
Explanation
After removing duplicates, the unique elements are 1, 2, and 3.
The function returns 3 because there are three unique elements.
Example 2
Input
10 0 0 1 1 1 2 2 3 3 4
Output
5 0 1 2 3 4
Explanation
Each unique element appears only once in the first five positions of the array.
Constraints
Hints:
Hint 1
Since the array is already sorted, duplicate elements always appear next to each other.
Hint 2
Use two pointers. One pointer scans the array while the other keeps track of the position to place the next unique element.
Author & Technical Reviewer
Technically reviewed by: ExamAdda Technical Review Team
Technical Reviewers, ExamAdda
Software engineers at ExamAdda who check every article's definitions, complexity claims and code examples before and after publishing.
Published
Jul 29, 2026
Last updated
Aug 6, 2026
Content Verification Methodology
Definitions and complexity claims were checked against authoritative computer-science references. Code examples were compiled and tested with standard, boundary and edge-case inputs.
Expected Output