Remove Duplicates from Sorted Array

Remove Duplicates from Sorted Array is a Easy Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Two Pointers pattern, in the In-place Array Modification subpattern.

Problem statement

Given an integer array nums sorted in non-decreasing order, remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums.

Consider the number of unique elements of nums to be k, to get accepted, you need to do the following things:

- Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums.

- Return k.

Custom Judge:

The judge will test your solution with the following code:

int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length

int k = removeDuplicates(nums); // Calls your implementation

assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; }

If all assertions pass, then your solution will be accepted.

Example 1:

Input: nums = [1,1,2] Output: 2, nums = [1,2,] Explanation: Your function should return k = 2, with the first two elements of nums being 1 and 2 respectively. It does not matter what you leave beyond the returned k (hence they are underscores).

Example 2:

Input: nums = [0,0,1,1,1,2,2,3,3,4] Output: 5, nums = [0,1,2,3,4,,,,,] Explanation: Your function should return k = 5, with the first five elements of nums being 0, 1, 2, 3, and 4 respectively. It does not matter what you leave beyond the returned k (hence they are underscores).

Constraints:

- 1 <= nums.length <= 3 104

- -100 <= nums[i] <= 100

- nums is sorted in non-decreasing order.

Topics and companies

Topics: Array, Two Pointers.

Reported in interviews at Google, Facebook, Amazon, Microsoft.

How to practise Remove Duplicates from Sorted Array on Thita.ai

Starter code is provided in C, 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) time and O(1) space.

Open Remove Duplicates from Sorted Array in the code editor, or read the Remove Duplicates from Sorted Array editorial for a worked solution with its approach and complexity analysis.

Where Remove Duplicates from Sorted Array sits in the DSA pattern sheet

Problems related to Remove Duplicates from Sorted Array

Other problems that use the same In-place Array Modification and Two Pointers techniques:

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