Lists as Stacks

A stack is a data structure that follows the Last-In-First-Out (LIFO) principle. Think of a stack of plates: you add plates to the top and remove from the top. The last plate you put on is the first one you take off. Python lists naturally support stack operations efficiently. Stack Operations Items are popped in reverse order: "third" first (last in, first out), then "second". The stack shrinks from the end. This LIFO behavior is what defines a stack. Undo Functionality Example Stacks are commonly used to implement undo functionality in applications. Each action saves the previous state. Undoing restores the most recent saved state. Balanced Parens Example Checking for balanced parentheses is a classic stack problem. For each opening bracket, push it onto the stack. For each closing brack