Evaluate Reverse Polish Notation

You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation. Evaluate the expression and return an integer.

Valid Operators: +, -, *, /. Integer division truncates toward zero.

Example:

• Input: ["2","1","+","3","*"]
• Logic: ((2 + 1) * 3) = 9
• Output: 9
• Input: ["4","13","5","/","+"]
• Logic: (4 + (13 / 5)) = 6

RPN is perfectly suited for a Stack.

1. Initialize an empty stack.
2. Iterate through each token.
3. If token is a number, push it to the stack.
4. If token is an operator:
   • pop the top two elements (say b is top, a is next).
   • Perform a <op> b.
   • push the result back.
5. Final result is the only element left in the stack.

Visualize how operands wait on the stack until an operator consumes them.