Reverse Polish Notation

Problem Description

Evaluate the value of an arithmetic expression in Reverse Polish Notation (RPN).

Valid operators are +, -, *, and /. Each operand may be an integer or another expression.

Note: Division between two integers should truncate toward zero.

It is guaranteed that the given RPN expression is always valid. That means the expression would always evaluate to a result, and there will not be any division by zero operation.

Examples

Example 1:

Input: tokens = ["2","1","+","3","*"]
Output: 9
Explanation: ((2 + 1) * 3) = 9

Example 2:

Input: tokens = ["4","13","5","/","+"]
Output: 6
Explanation: (4 + (13 / 5)) = 6

Example 3:

Input: tokens = ["10","6","9","3","+","-11","*","/","*","17","+","5","+"]
Output: 22

Constraints

• 1 <= tokens.length <= 10^4
• tokens[i] is either an operator: "+", "-", "*", or "/", or an integer in the range [-200, 200].

Hint

Think about what data structure allows you to easily access the most recently added elements.