Question 1

Which data structure follows LIFO (Last In, First Out)?

Accepted Answer

Stack. A stack follows LIFO — the last element pushed is the first one popped. Think of a stack of plates: you add and remove from the top.

Question 2

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

Accepted Answer

O(1). Array indexing is O(1) — constant time — because the address is calculated directly as: base address + index × element size.

Question 3

Which data structure follows FIFO (First In, First Out)?

Accepted Answer

Queue. A queue follows FIFO — the first element enqueued is the first dequeued. Think of a line at a counter: first in, first served.

Question 4

What does Big O notation describe?

Accepted Answer

The upper bound on an algorithm's growth rate as input grows. Big O describes the worst-case growth rate of an algorithm's time or space as input size increases. It ignores constants and low-order terms.

Question 5

What is the worst-case time complexity of binary search?

Accepted Answer

O(log n). Binary search halves the search space at each step, giving O(log n). For 1 million elements it takes at most ~20 comparisons.

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