Evaluate Reverse Polish Notation

Problem Evaluate an arithmetic expression given in Reverse Polish Notation (postfix). Tokens are integers and the operators +, -, *, /. Each operator applies to the two most recent operands.

Input / Output

• Input: a list of string tokens in RPN.
• Output: the integer result of evaluating the expression.

Constraints

• The expression is valid.
• Division truncates toward zero (clarify).
• Operands and intermediate results fit in a 64-bit integer.

Example

• ["2","1","+","3","*"] -> 9 ((2+1)*3)
• ["4","13","5","/","+"] -> 6 (4 + 13/5)