Evaluate Reverse Polish Notation
Recognize the pattern
Brute force idea
A straightforward first read of Evaluate Reverse Polish Notation is this: No better approach exists — stack is the natural solution. That instinct is useful because it follows the prompt literally, but it usually keeps revisiting work the problem is begging you to organize.
Better approach
A calmer way to see Evaluate Reverse Polish Notation is this: Push numbers onto stack; when you see an operator, pop two operands, compute, push result. The goal is not to be clever for its own sake, but to remember the one relationship that keeps the solution grounded as you move forward.
Key invariant
The truth you want to protect throughout Evaluate Reverse Polish Notation is this: The stack always contains operands waiting for their operator. If that remains true after every update, the rest of the reasoning has a stable place to stand.
Watch out for
The trap in Evaluate Reverse Polish Notation usually looks like this: Operand order matters for subtraction and division — second popped is left operand. When the code becomes mechanical before the idea is clear, small edge cases start breaking the whole story.