package main

import "fmt"

func main() {
    s := "2[moonfdd3[a]]2[]"
    ret := decodeString(s)
    fmt.Println(ret)
}

func decodeString(s string) string {
    str := []byte(s)
    return process(str, 0).ans
}

type Info struct {
    ans  string
    stop int
}

func NewInfo(a string, e int) *Info {
    ret := &Info{}
    ret.ans = a
    ret.stop = e
    return ret
}

// s[i....]  何时停？遇到   ']'  或者遇到 s的终止位置，停止
// 返回Info
// 0) 串
// 1) 算到了哪
func process(s []byte, i int) *Info {
    //StringBuilder ans = new StringBuilder();
    ans := make([]byte, 0)
    count := 0
    for i < len(s) && s[i] != ']' {
        if (s[i] >= 'a' && s[i] <= 'z') || (s[i] >= 'A' && s[i] <= 'Z') {
            ans.append(s[i++]);
            ans = append(ans, s[i])
            i++
        } else if s[i] >= '0' && s[i] <= '9' {
            count = count*10 + int(s[i]) - int('0')
            i++
        } else { // str[index] = '['
            next := process(s, i+1)
            //ans.append(timesString(count, next.ans));
            ans = append(ans, timesString(count, next.ans)...)
            count = 0
            i = next.stop + 1
        }
    }

    return NewInfo(string(ans), i)
}

func timesString(times int, str string) string {
    ans := make([]byte, 0)
    for i := 0; i < times; i++ {
        ans = append(ans, str...)
    }
    return string(ans)
}