## What is it? Convert an infix expression (standard math notation, e.g. `A+B*C`) to postfix notation (e.g. `ABC*+`) also known as Reverse Polish Notation (RPN). Postfix is easier for computers to evaluate. ## How it works **Shunting-Yard Algorithm (Dijkstra):** - Scan left to right - **Operand** → output it - **Operator** → pop operators from the stack to output while they have higher or equal precedence, then push current - **`(`** → push to stack - **`)`** → pop to output until `(` is found; discard both parentheses - At the end, pop all remaining operators from stack to output ## When to use - Expression evaluation without parentheses - Calculator implementations - Compiler intermediate representation ## Key Points - Postfix evaluation: push operands, pop two on operator, push result - Precedence: `*`, `/` > `+`, `-`; `^` is right-associative - No parentheses in output — operator ordering handles precedence implicitly