1935_후위 표기식2.swift

import Foundation

enum OperType: Character {
    case plus = "+"
    case minus = "-"
    case multiply = "*"
    case divisor = "/"
    
    func calculate(_ n1: Double, _ n2: Double) -> Double {
        switch self {
        case .plus: return n1 + n2
        case .minus: return n2 - n1
        case .multiply: return n1 * n2
        case .divisor: return n2 / n1
        }
    }
}

let n = Int(readLine()!)!
let command = readLine()!
var dict: [Character: Double] = [:]
var numStack: [Double] = []

for i in 0..<n {
    dict[Character(UnicodeScalar(i + 65)!)] = Double(readLine()!)!
}

for cmd in command {
    if let oper = OperType(rawValue: cmd) {
        numStack.append(oper.calculate(numStack.removeLast(), numStack.removeLast()))
    } else {
        numStack.append(dict[cmd, default: 0])
    }
}
print(String(format: "%.2f", numStack.last!))