Remove Duplicates from Sorted Array - LeetCode Java Solution

👋 Introduction

Welcome to my LeetCode Solutions in Java series! In each post, I’ll break down one LeetCode problem with a clear explanation, Java code, and a complexity analysis.
Today we will solve the problem: Remove Duplicates from Sorted Array.

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🔍 Problem Statement

Given: A sorted array nums in non-decreasing order.

Task: Remove duplicates from sorted array, so that unique element appears only once.

Return: The new length k, where first k elements in nums are unique.

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).

→ View on LeetCode

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💡 Approach

Here, we will make use of two pointers - one to keep track of the current element and another one to keep the reference.

• Initialise reference = 0;

• Loop current from 1 to end

  • If nums[current] != nums[reference]:

    • Increment reference

    • Set nums[reference] = nums[current] (move unique forward)

• Return reference + 1 as the new length of the array.

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🧠 Java Code

class Solution {
    public int removeDuplicates(int[] nums) {
        int reference = 0;
        for (int current = 1; current < nums.length; current++) {
            if (nums[current] != nums[reference]) {
                reference++;
                nums[reference] = nums[current];
            }
        }
        return reference + 1;
    }
}

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⏱️ Time Complexity

✅ Best & Worst Case: O(n)

• We iterate through the array once → O(n)

• There are no other operations, hence total time complexity → O(n)

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🧮 Space Complexity

✅ Best & Worst Case: O(1)

• We are introducing only two variables despite of the size of input array.

• Hence, space complexity is O(1)

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🧩 Related Topics

• Array

• Two Pointers

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Stay tuned for the next problem in this series!