새로 알아간 것들

if - 삼항연산자 구현 꼭 기억하기

array == [] ? [-1] : array

reduce

monthDay[0..<a-1].reduce(0, +) + b

stack 구현하기

import Foundation

struct Stack {
    private var items: [String] = []
    
    func peek() -> String {
        guard let topElement = items.first else { fatalError("This stack is empty.") }
        return topElement
    }
    
    mutating func pop() -> String {
        return items.removeFirst()
    }
  
    mutating func push(_ element: String) {
        items.insert(element, at: 0)
    }
}

extension Stack: CustomStringConvertible {
    var description: String {
        let topDivider = "---Stack---\n"
        let bottomDivider = "\n-----------\n"

        let stackElements = array.joined(separator: "\n")

        return topDivider + stackElements + bottomDivider
    }
}

reference