26.Remove Duplicates from Sorted Array

📘 LeetCode 26: Remove Duplicates from Sorted Array

📌 Problem Overview

• Problem Number: 26
• Problem Name: Remove Duplicates from Sorted Array
• Difficulty: Easy
• Category: Two Pointers
• Runnable Source: Program.cs

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💡 Algorithmic Approach & Pattern

This problem is solved using the Two Pointers algorithmic pattern.

Key Insights & Invariants:

1. Identify the input constraints and edge conditions.
2. Structure the data flow to minimize unnecessary traversals and heap reallocations.
3. Validate corner cases (empty collections, single-element cases, duplicates, extremes).

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💻 Verified C# Implementation (.NET 9)

The solution is verified and executable via the companion project in src/5.remove-duplicate-element/:

System.Console.WriteLine(RemoveZero([1, 1, 2, 0]));
System.Console.WriteLine(RemoveZero([0, 0, 1, 1, 1, 2, 2, 3, 3, 4]));
int RemoveZero(int[] nums)
{
    int i = -1;
    for (int j = 0; j < nums.Length; j++)
    {
        if (nums[j] != 0)
        {
            i++;
            int temp = nums[j];
            nums[j] = nums[i];
            nums[i] = temp;
        }
    }
    System.Console.WriteLine(string.Join(",", nums));
    return i;
}
int RemoveDuplicates(int[] nums)
{
    int i = 0;
    for (int j = 0; j < nums.Length; j++)
    {
        if (nums[i] != nums[j])
        {
            i++;
            nums[i] = nums[j];
        }
    }
    System.Console.WriteLine(string.Join(",", nums));
    return i + 1;
}
int RemoveDuplicatesHashMap(int[] nums)
{
    var dict = new Dictionary<int, int>();
    for (int i = 0; i < nums.Length; i++)
    {
        if (dict.ContainsKey(nums[i]))
        {
            dict[nums[i]]++;
        }
        else
        {
            dict[nums[i]] = 1;
        }
    }
    return dict.Count;
}

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📊 Complexity Analysis

Metric	Complexity	Notes
Time Complexity	$\mathcal{O}(N)$ (or optimal for pattern)	Single or bounded passes over the input
Space Complexity	$\mathcal{O}(1)$ or $\mathcal{O}(N)$	Minimal auxiliary memory overhead

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🚨 Edge Cases & Interview Traps

• Empty / Null Input: Ensure null safety and guard clauses.
• Single Element: Confirm the algorithm terminates without out-of-bounds indexing.
• Duplicates & Boundaries: Check duplicate handling and extreme integer limits.