Dsa Two Pointers Remove Dups

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

Fix remove duplicates ii errors when allow at most two duplicates instead of one.

Quick Fix

Wrong

def remove_dups(a):
    if not a: return 0
    w=1; cnt=1
    for r in range(1,len(a)):
        if a[r]==a[r-1]: cnt+=1
        else: cnt=1
        if cnt<=2: a[w]=a[r]; w+=1
    return w

Allows at most 2 of each value. Common variant of remove duplicates.

Right

def remove_dups(a):
    if len(a)<=2: return len(a)
    w=2
    for r in range(2,len(a)):
        if a[r]!=a[w-2]:
            a[w]=a[r]; w+=1
    return w

[1,1,1,2,2,3] -> 5 (1,1,2,2,3). O(n) time, O(1) space.

Prevention

Write pointer starting at 2. Compare current with write-2 position.

DodaTech Tools

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FAQ