535.encode-and-decode-tinyurl.md

535. Encode and Decode TinyURL

Hash Table

We need to record the relationship between the long URL and the short URL and vice versa.

class Codec() {
    private val long2Short = HashMap<String, String>()
    private val short2Long = HashMap<String, String>()
    private val chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
    private val shortUrlLength = 6

    // Encodes a URL to a shortened URL.
    fun encode(longUrl: String): String {
        if (longUrl in long2Short) return long2Short[longUrl]!!
        var shortUrl: String
        do {
            shortUrl = generateShortUrl(longUrl)
        } while (shortUrl in short2Long)
        long2Short[longUrl] = shortUrl
        short2Long[shortUrl] = longUrl
        return shortUrl
    }

    // Decodes a shortened URL to its original URL.
    fun decode(shortUrl: String): String {
        return short2Long[shortUrl] ?: ""
    }

    private fun generateShortUrl(longUrl: String): String {
        val url = StringBuilder()
        repeat(shortUrlLength) {
            val index = (Math.random() * chars.length).toInt()
            url.append(chars[index])
        }
        return url.toString()
    }
}