WBJECA 2025 — Computer PYQ

To understand why, we look at the underlying data structure requirements for each algorithm. A Stack follows the LIFO (Last-In-First-Out) principle, whereas a Queue follows the FIFO (First-In-First-Out) principle.

The operational logic for these structures can be represented as:

• Stack: $\text{Push}(item)\to \text{Pop}(item)$ (LIFO)

• Queue: $\text{Enqueue}(item)\to \text{Dequeue}(item)$ (FIFO)

Here is how the options align:

• (A), (B), and (C) are classic applications of a Stack because they require reversing the order of operations or keeping track of the most recent state.

• (D) Breadth-first search (BFS) is fundamentally designed to visit nodes level-by-level, which requires the FIFO behavior of a Queue. Mathematically, for a graph $G$ with vertices $V$, BFS ensures:

  $$\text{Distance}(v_1)\le \text{Distance}(v_2)$$

  for any nodes processed sequentially in the queue.