Remove Duplicates from Sorted Array Two Pointer in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main goal of the 'Remove Duplicates from Sorted Array Two Pointer' technique?

To remove duplicate elements from a sorted array in-place, so that each element appears only once, and return the new length of the array.

beginner

Why does the two-pointer approach work efficiently for removing duplicates in a sorted array?

Because the array is sorted, duplicates appear consecutively. One pointer tracks the position to insert unique elements, and the other scans through the array to find new unique elements.

beginner

In the two-pointer method, what do the pointers usually represent?

One pointer (slow) marks the position of the last unique element, and the other pointer (fast) scans ahead to find the next unique element.

beginner

What is the time complexity of removing duplicates from a sorted array using the two-pointer technique?

O(n), where n is the number of elements in the array, because each element is visited at most once.

beginner

What does 'in-place' mean in the context of removing duplicates from an array?

It means modifying the original array without using extra space for another array, except for a few variables.

What is the initial position of the slow pointer in the two-pointer approach for removing duplicates?

A 0

B 1

C array length - 1

D array length

The slow pointer starts at index 0, pointing to the first unique element.

When do we move the slow pointer forward in the two-pointer method?

A At every iteration regardless

B When the fast pointer finds a duplicate

C Only at the end

D When the fast pointer finds a new unique element

The slow pointer moves forward only when the fast pointer finds a new unique element to place.

What is the space complexity of the two-pointer approach for removing duplicates from a sorted array?

A O(1)

B O(n)

C O(log n)

D O(n^2)

The approach uses constant extra space, modifying the array in-place.

What happens if the input array is empty?

A Return -1 as error

B Return 1 as the length

C Return 0 as the length

D Crash

If the array is empty, there are no elements, so the length after removing duplicates is 0.

Which of these arrays after removing duplicates using two pointers will have length 3?

A [1, 2, 3, 4]

B [1, 1, 2, 3, 3]

C [1, 1, 1, 1]

D []

After removing duplicates, [1, 1, 2, 3, 3] becomes [1, 2, 3], length 3.

Explain how the two-pointer technique removes duplicates from a sorted array in-place.

Think about how two pointers move and interact in the array.

Describe the advantages of using the two-pointer approach for removing duplicates in a sorted array.

Focus on time, space, and why sorting helps.