Data Structures Arrays and Strings

Question 1

What is the time complexity of accessing an element in an array by index?

Accepted Answer

O(1)

Answer

Array elements are stored in contiguous memory locations, so index-based access is always O(1) constant time.

Question 2

Which array traversal technique uses two pointers moving toward each other from both ends?

Accepted Answer

Two-pointer technique

Answer

The two-pointer technique places one pointer at the start and one at the end, moving them toward each other to solve problems efficiently.

Question 3

What is the worst-case time complexity of searching for an element in an unsorted array?

Accepted Answer

O(n)

Answer

In the worst case, you must examine every element in an unsorted array, giving O(n) linear time complexity.

Question 4

Which operation is most expensive in a dynamic array when it needs to resize?

Accepted Answer

Appending when capacity is full

Answer

When a dynamic array exceeds capacity, all existing elements must be copied to a new larger array, making it an O(n) operation.

Question 5

What does the sliding window technique optimize when processing subarrays or substrings?

Accepted Answer

Avoiding nested loops by reusing previous computations

Answer

The sliding window technique maintains a running result as the window moves, reducing time complexity from O(n²) to O(n).

Data Structures Practice Test