Evaluate Reverse Polish Notation

reverse_polish_notation.swift

class Solution {
    func evalRPN(_ tokens: [String]) -> Int {
        var stack = [Int]()
        var operators = "+-/*"
        for token in tokens {
            if operators.contains(token) {
                var result = 0 
                let second = stack.popLast()!
                let first = stack.popLast()!
                switch token {
                    case "+":
                        result = first + second
                    case "-":
                        result = first - second
                    case "*":
                        result = first * second
                    default:
                        result = first/second
                }
                stack.append(result)
            }
            else if let value = Int(token){
                stack.append(value)
            }
        }
        return stack[0]
    }
}