How to Fix Remove Duplicates from Sorted Array Errors

In this tutorial, you'll learn about How to Fix Remove Duplicates from Sorted Array Errors. We cover key concepts, practical examples, and best practices.

Fix remove duplicates from sorted array errors when two-pointer miscounts or in-place modification fails.

Quick Fix

Wrong

def remove_duplicates(nums):
    return len(set(nums))

Wrong: returns correct count but doesn't modify array in-place.

Right

def remove_duplicates(nums):
    if not nums: return 0
    w=1
    for r in range(1,len(nums)):
        if nums[r]!=nums[r-1]: nums[w]=nums[r]; w+=1
    return w

[0,0,1,1,1,2,2,3,3,4] -> 5, nums[:5]=[0,1,2,3,4]. O(n).

Prevention

Use read/write pointers. Compare with previous element. Start write at 1.

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