You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation.

Evaluate the expression. Return an integer that represents the value of the expression.

Note that:

• The valid operators are ‘+’, ‘-‘, ‘*’, and ‘/’.
• Each operand may be an integer or another expression.
• The division between two integers always truncates toward zero.
• There will not be any division by zero.
• The input represents a valid arithmetic expression in a reverse polish notation.
• The answer and all the intermediate calculations can be represented in a 32-bit integer.

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
• Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5
  = ((10 * (6 / (12 * -11))) + 17) + 5
  = ((10 * (6 / -132)) + 17) + 5
  = ((10 * 0) + 17) + 5
  = (0 + 17) + 5
  = 17 + 5
  = 22
  

Constraints:

• 1 <= tokens.length <= 10⁴
• tokens[i] is either an operator: “+”, “-“, “*”, or “/”, or an integer in the range [-200, 200].