Question

Suppose you have an empty stack, and you execute the following operations:

push(1);
push(2);
push(3);
peek()
pop();
push(1);
pop();
pop();
What are the contents of the stack? Be sure to clearly indicate the top and bottom of the stack.

Answer 1

The final content of the stack after executing the operations push(1), push(2), push(3), peek(), pop(), push(1), pop(), and pop() is only one element with the value 1.

Step-by-step explanation:

The question pertains to the concept of a stack, which is a fundamental data structure in Computers and Technology. A stack operates on the Last In, First Out (LIFO) principle. This means that the last element pushed onto the stack is the first one to be popped off. Let's examine the operations one by one on an initially empty stack and see what the content of the stack is after each operation:

• push(1): Stack now has 1 on top.
• push(2): Stack now has 2 on top, 1 at the bottom.
• push(3): Stack now has 3 on top, 2 in the middle, 1 at the bottom.
• peek(): Returns the top element without removing it, which is 3. The stack remains unchanged.
• pop(): Removes the top element, which is 3. Stack now has 2 on top, 1 at the bottom.
• push(1): Stack now has a second 1 on top, 2 in the middle, and the original 1 at the bottom.
• pop(): Removes the top element, which is the second 1. Stack now has 2 on top, original 1 at the bottom.
• pop(): Removes the top element, which is 2. Stack is left with just the original 1.

After performing all the given operations, the contents of the stack are as follows, with the top of the stack mentioned first:

• 1 (Top)

The stack has only one element left, which is the number 1. All other elements have been popped out of the stack.