백준 계단 오기 2579번

import Foundation

let n = Int(readLine()!)!

var stairs: [Int] = []

(0..<n).forEach { _ in
    let stair = Int(readLine()!)!
    stairs.append(stair)
}


func solution() {
    if isOnenTwo() { return }
    
    var dp: [Int] = Array(repeating: 0, count: n)
    
    dp[0] = stairs[0]
    dp[1] = stairs[0] + stairs[1]
    dp[2] = max(stairs[0] + stairs[2], stairs[1] + stairs[2])
    
    for i in (3..<n) {
        dp[i] = max(dp[i-3] + stairs[i-1] + stairs[i], dp[i-2] + stairs[i])
    }
    
    print(dp.last!)
}

func isOnenTwo() -> Bool {
    if n == 1 {
        print( stairs[0] )
        return true
    }
    
    if n == 2 {
        print( stairs[0] + stairs[1] )
        return true
    }
    
    return false
}

solution()