Remove Duplicates from Sorted Array Two Pointer in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the slow pointer for the two-pointer technique.

DSA Python

def remove_duplicates(nums):
    if not nums:
        return 0
    slow = [1]
    for fast in range(1, len(nums)):
        if nums[fast] != nums[slow]:
            slow += 1
            nums[slow] = nums[fast]
    return slow + 1

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A0

B1

C-1

Dlen(nums)

Attempts:

3 left

💡 Hint

Common Mistakes

Starting slow at 1 causes skipping the first element.

Using -1 causes index errors.

The slow pointer starts at index 0 to track the position of the last unique element.

2fill in blank

medium

Complete the code to check if the current fast pointer element is different from the slow pointer element.

DSA Python

def remove_duplicates(nums):
    if not nums:
        return 0
    slow = 0
    for fast in range(1, len(nums)):
        if nums[fast] [1] nums[slow]:
            slow += 1
            nums[slow] = nums[fast]
    return slow + 1

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A!=

B<

C==

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' causes duplicates to be copied.

Using '<' or '>' is incorrect for equality check.

We want to move the slow pointer only when we find a new unique element, so we check if nums[fast] is not equal to nums[slow].

3fill in blank

hard

Fix the error in the code to correctly update the slow pointer and assign the new unique element.

DSA Python

def remove_duplicates(nums):
    if not nums:
        return 0
    slow = 0
    for fast in range(1, len(nums)):
        if nums[fast] != nums[slow]:
            [1]  # increment slow pointer
            nums[slow] = nums[fast]
    return slow + 1

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Afast += 1

Bslow = fast

Cslow += 1

Dslow -= 1

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning slow = fast skips elements.

Incrementing fast inside loop causes errors.

The slow pointer should be incremented by 1 to move to the next position for the unique element.

4fill in blank

hard

Fill both blanks to complete the function that returns the length of the array after removing duplicates.

DSA Python

def remove_duplicates(nums):
    if not nums:
        return 0
    slow = 0
    for fast in range(1, len(nums)):
        if nums[fast] != nums[slow]:
            slow [1] 1
            nums[slow] = nums[fast]
    return slow [2] 1

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A+=

B-=

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-=' decreases slow incorrectly.

Returning slow - 1 gives wrong length.

We increment slow by 1 using '+=' and return slow + 1 because the length is index + 1.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps each unique number to its index after removing duplicates.

DSA Python

def map_unique_indices(nums):
    length = remove_duplicates(nums)
    return { [1]: [2] for [3] in range(length) }

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Anums[i]

Bi

Dnum

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'num' causes NameError as 'num' is not defined.

Mixing variable names like using 'i' for key maps index to index.

We map each unique number nums[i] to its index i, iterating i in range(length).