Static Arrays

Remove Duplicates from sorted Array

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:

1. 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.
2. The remaining elements of nums are not important, as well as the size of nums.
3. Return k.

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).

Code

import java.util.*;

class Solution {
    public int removeDuplicates(int[] nums) {
        // Use a Set to store unique elements as Set only allows unique values, That was my first thought on this problem
        Set<Integer> set = new HashSet<>();
        
        // Then we add all the elements of array to Set , so that only unique elements remain
        for(int num : nums) {
            set.add(num);
        }
        
        // using a for loop and a post-increment op resize the current nums array with the size of elements in set and copy elements back to array
        int i = 0;
        for(int n : set) {
            nums[i++] = n;
        }
        
        // Finally sort using the Arrays.sort() method. 
        Arrays.sort(nums, 0, set.size());
        
        // to return the number of unique elements we return the size of the set
        return set.size();
    }
}