Evaluate Reverse Polish Notation

Problem Evaluate an arithmetic expression given in Reverse Polish (postfix) Notation. Tokens are integers and the operators +, −, *, /. Division truncates toward zero.

Input / Output

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

Constraints

• The expression is always valid.
• Operands and intermediate results fit in a 32-bit integer; division truncates toward zero.

Example

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