Stack

PushedPopping

stack

LIFO — last in, first out

↓ top

stack is empty

↑ bottom (fixed)

pseudocode

push(x)
  top++; a[top] = x
pop()
  x = a[top]; top--
  return x

Frame 1 / 12

Start

empty stack

Speed4

Operations

Comma-separated: "push N" or "pop". 1–12 operations, values 1–99.