프로그래머스 - 영어 끝말잇기

import Foundation

func solution(_ n:Int, _ words:[String]) -> [Int] {
    
    var stack: [String] = []
    var previous: Character = words.first!.last!
    var num = 1
    var cycle = 1
    for word in words {
        
        if num > n {
            num = 1
            cycle += 1
        }
        
        if stack.isEmpty {
            stack.append(word)
        } else {
            if stack.contains(word) || word.first != previous {
                return [num, cycle]
            } else {
                stack.append(word)
            }
        }
        
        num += 1
        previous = word.last!
    }
    
    return [0, 0]
}