Array Reversal Techniques in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main idea behind reversing an array in place?

Swapping elements from the start and end of the array moving towards the center until all elements are reversed.

beginner

Explain the two-pointer technique for array reversal.

Use two pointers: one at the beginning and one at the end of the array. Swap the elements at these pointers and move them towards each other until they meet or cross.

beginner

What is the time complexity of reversing an array using the two-pointer method?

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

intermediate

Why is reversing an array in place considered space efficient?

Because it does not require extra space proportional to the array size; it only uses a few variables for swapping.

beginner

Describe a method to reverse an array using an auxiliary array.

Create a new array of the same size, copy elements from the original array starting from the end to the beginning, then copy back to the original array if needed.

Which technique swaps elements from both ends moving towards the center to reverse an array?

A Bubble sort

B Divide and conquer

C Linear search

D Two-pointer technique

The two-pointer technique uses two indices at the start and end to swap elements until the array is reversed.

What is the space complexity of reversing an array in place?

A O(log n)

B O(n)

C O(1)

D O(n^2)

In-place reversal uses constant extra space, so space complexity is O(1).

If an array has 10 elements, how many swaps are needed to reverse it using the two-pointer method?

A 5

B 10

C 9

D 20

Only half the elements need to be swapped, so 5 swaps for 10 elements.

Which of the following is NOT a correct step in reversing an array using an auxiliary array?

A Swap elements in the original array without extra space

B Copy elements back from the auxiliary array to the original array

C Copy elements from the original array to the auxiliary array in reverse order

D Create a new array of the same size as the original

Swapping without extra space is the in-place method, not the auxiliary array method.

What is the time complexity of reversing an array using an auxiliary array?

A O(n^2)

B O(n)

C O(1)

D O(n log n)

Copying elements to and from the auxiliary array takes linear time, O(n).

Explain how to reverse an array in place using the two-pointer technique.

Think about swapping pairs from opposite ends.

Describe the differences between reversing an array in place and using an auxiliary array.

Consider space usage and steps involved.