README.md

Implement a Queue using two Stacks

Challenge

Create a PseudoQueue class without using an existing queue. The class should implement a standard queue interface using the methods below but will internally utilize only two Stack objects.

Use only push, pop, and peek methods of the Stack instances.

The class should have the following methods.

• enqueue(value) - Inserts value into the PseudoQueue using a FIFO approach.
• dequeue() - Extracts a value from the PseudoQueue, using a FIFO approach.

Approach & Efficiency

In order to get FIFO behavior from FILO/LIFO stacks, we need to move all values from one internal stack to the other whenever a switch is made from enqueuing to dequeuing. We can think of the two stacks as inStack and outStack.

enqueue(value)

• move all values from outStack to inStack
  • while outStack.peek() is not null
    • inStack.push(outStack.pop())
• inStack.push(value)

dequeue()

• move all values from inStack to outStack
  • while inStack.peek() is not null
    • outStack.push(inStack.pop())
• return value of outStack.pop()

Solution

Problem Domain

Approach, Visual, and Pseudo-code

Whiteboard Code

Code