Remove Duplicates from Sorted Array

This is a Leet Code problem solved in Java, the problem description is:

Given a sorted array nums, remove the duplicates in-place such that each element appear only once and return the new length.

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

Example 1:

Given nums = [1,1,2],

Your function should return length = 2, with the first two elements of nums being 1 and 2 respectively. It doesn't matter what you leave beyond the returned length.

Example 2:

Given nums = [0,0,1,1,1,2,2,3,3,4],

Your function should return length = 5, with the first five elements of nums being modified to 0, 1, 2, 3, and 4 respectively. It doesn't matter what values are set beyond the returned length.


Confused why the returned value is an integer but your answer is an array?

Note that the input array is passed in by reference, which means modification to the input array will be known to the caller as well.

Internally you can think of this:

// nums is passed in by reference. (i.e., without making a copy)
int len = removeDuplicates(nums);

// any modification to nums in your function would be known by the caller.
// using the length returned by your function, it prints the first len elements.
for (int i = 0; i < len; i++) {


As the input Array length is predetermined, it cannot be changed. Hence, the problem statement says ‘It doesn’t matter what values are set beyond the returned length.’. This means in an input array {1,1,2}, after removing the duplicates the return array could be {1,2,2} which is accepted. The number of unique integer is 2 which means the system will only check the first 2 elements of the array {1,2} and the third element is ignored for the test.


  • New List cannot be created, so we will modify the input array.
  • No inbuilt functions are used.
  • This is the simplest and one of the fastest solution. Here, the length of the unique elements is stored in int y.


class Solution {
    public int removeDuplicates(int[] nums) {
        int y=1;
        for(int i=1; i<nums.length; i++){
                nums[y] = nums[i];
        return y;

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