백준 - 오큰수 (17298)

let N = Int(readLine()!)!
let arr = readLine()!.split(separator: " ").map{ Int(String($0))! }
var answer = Array(repeating: -1, count: N)
var stack = [Int]()

for (index, number) in arr.enumerated() {
    while !stack.isEmpty && arr[stack.last!] < number {
        answer[stack.last!] = number
        stack.removeLast()
    }
    stack.append(index)
}

print(answer.map{String($0)}.joined(separator: " "))