G4G0-2/Data Structures/AI Notes/Stack.md

Overview

• A stack is ta LIFO list. Meaning "last in first out"
• Access is allowed only from one end of the stack
  • adding an item is called pulsing the stack
  • retrieving an item is called popping the stack

Typical Uses

• Parentheses matching; ()), or (())
  • compiler's syntax check for matching braces is implemented by using stack
• The simplest application of a stack is to reverse a word.
  • You push a given word to stack - letter by letter - and then pop letters from the stack.
• Another application is an "undo" mechanism in text editors; -this operation is accomplished by keeping all text changes in a stack

Parenthesis Count

• Methodology (logical steps to solve the problem):
  • scan expression from left to right;
  • when a left parenthesis is encountered, add its position to the stack;
• when a right parenthesis is encountered, remove matching position from stack (more example in a moment).

Try-catch-throw

• When you enter a try block, push the address of this block onto a stack. \
• When an exception is thrown, pop the try block that is at the top of the stack; if the stack is empty, terminate the program.
• If the popped try block has no matching catch block, go back to the previous step.
• If the popped try block has a matching catch block, execute the matching catch block.