What is the best approach to solve Remove Duplicates from Sorted Array?

The optimal approach for Remove Duplicates from Sorted Array is the "Optimal — Two Pointers (In-Place)" technique. It runs in O(n) time and uses O(1) space. slow points to the last unique element placed. fast scans ahead. When nums[fast] != nums[slow], a new unique element is found — advance slow and overwrite. Since the array is sorted, duplicates are al

What is the time complexity of Remove Duplicates from Sorted Array?

The optimal solution for Remove Duplicates from Sorted Array has a time complexity of O(n) and a space complexity of O(1), achieved using the Two Pointers pattern.

Is Remove Duplicates from Sorted Array a Easy LeetCode problem?

Yes, LeetCode #26 (Remove Duplicates from Sorted Array) is rated Easy. It uses the Two Pointers pattern and is commonly asked in interviews at Microsoft, Google, Amazon.

How to solve Remove Duplicates from Sorted Array in Python, Java, C++, and JavaScript?

LumiChats provides complete solutions for Remove Duplicates from Sorted Array in Python, Java, C++, and JavaScript, along with step-by-step visual animations and time/space complexity analysis. All solutions are free to view.

#26EasyTwo Pointers

Remove Duplicates from Sorted Array

In-place deduplication of a sorted array using two pointers.

MicrosoftGoogleAmazonAdobe

Problem Statement

Given a sorted integer array nums, remove the duplicates in-place such that each unique element appears only once. Return the number of unique elements k. The first k elements of nums must contain the unique elements in order.

Examples

Example 1

Input:nums = [1,1,2]

Output:2, nums = [1,2,_]

Explanation: Two unique elements. First 2 positions hold [1,2].

Example 2

Input:nums = [0,0,1,1,1,2,2,3,3,4]

Output:5, nums = [0,1,2,3,4,_,_,_,_,_]

Constraints

1 ≤ nums.length ≤ 3 × 10⁴
-100 ≤ nums[i] ≤ 100
nums is sorted in non-decreasing order.

Solutions

Extra Array

TimeO(n)SpaceO(n)

Build a new array with only unique elements and copy back. Doesn't satisfy the in-place constraint.

Visual Animation

def removeDuplicates(nums: list[int]) -> int:
    unique = list(dict.fromkeys(nums))
    for i, v in enumerate(unique):
        nums[i] = v
    return len(unique)

Related Concepts

Deepen your understanding with these related topics from our AI Glossary:

Machine Learning Browse all 190+ concepts →

Deepen your understanding

Want to master the core concepts?

Our free AI Glossary covers 190+ topics — from Two Pointers to Dynamic Programming, Machine Learning, SQL, and more. Structured learning tracks for every level.

Browse AI Glossary All Problems

39+

AI Models

₹69

Per day used

Languages

Stuck? Ask AI to explain it step by step.

Ask Claude, GPT-4o, or Gemini to debug your code, generate test cases, or walk through the intuition. 39+ models. Pay only on days you use it — no subscription required.

Free to start · No credit card required to explore

Get Started Free

Back to all problems