//

// DecodeString.swift

// ConquerAlgorithm

//

// Created by Freelf on 2021/3/30.

// Copyright © 2021 Freelf. All rights reserved.

//

import Foundation

class DecodeStringSolution {

func decodeString(_ s: String) -> String {

var stack: [(Int, String)] = []

var result = ""

var mutil = 0

for char in s {

if char == "[" {

stack.append((mutil, result))

result = ""

mutil = 0

} else if char == "]" {

let (curMutil, lastRes) = stack.removeLast()

result = lastRes + String.init(repeating: result, count: curMutil)

} else if char.isWholeNumber {

mutil = mutil * 10 + char.wholeNumberValue!

} else {

result += String(char)

}

}

return result

}

func decodeString2(_ s: String) -> String {

func dfs(_ s: String, _ i: Int) -> (String, Int){

var res = "", mutil = 0, index = i

while index < s.count {

let curChar = s[s.index(s.startIndex, offsetBy: index)]

if curChar == "[" {

let (result, returnIndex) = dfs(s, index + 1)

res += String.init(repeating: result, count: mutil)

index = returnIndex

mutil = 0

} else if curChar == "]" {

return (res, index)

} else if curChar.isWholeNumber {

mutil = mutil * 10 + curChar.wholeNumberValue!

} else {

res.append(curChar)

}

index += 1

}

return (res, -1)

}

return dfs(s, 0).0

}

}