108. Queue with Stacks: Efficient Implementation Using Stack Operations

Objective: We know that Queue is FIFO (First-in-First-Out) and Stack is LIFO ( Last-in-First-Out).

Here our objective is to implement a queue using stacks.

Approach:

Take 2 Stacks, stack1 and stack2.
stack1 will be used as the back of the Queue and stack2 will be used as the front of the Queue.
Push() operations will be done on stack1, and peek() and pop() operations will be done on stack2.
When peek() and pop() are called, check if stack2 is empty, if yes then move all the elements from stack1 and push them into stack2.

Example:

Output:

POP from Queue 10