题目：

题解：

import "math/rand"

type Codec map[int]string

func Constructor() Codec {
    return Codec{}
}

func (c Codec) encode(longUrl string) string {
    for {
        key := rand.Int()
        if c[key] == "" {
            c[key] = longUrl
            return "http://tinyurl.com/" + strconv.Itoa(key)
        }
    }
}

func (c Codec) decode(shortUrl string) string {
    i := strings.LastIndexByte(shortUrl, '/')
    key, _ := strconv.Atoi(shortUrl[i+1:])
    return c[key]
}