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# 535.Encode-and-Decode-TinyURL

## 题目描述

Note: This is a companion problem to the System Design problem: Design TinyURL.
TinyURL is a URL shortening service where you enter a URL such as https://leetcode.com/problems/design-tinyurl and it returns a short URL such as http://tinyurl.com/4e9iAk.
Design the encode and decode methods for the TinyURL service. There is no restriction on how your encode/decode algorithm should work. You just need to ensure that a URL can be encoded to a tiny URL and the tiny URL can be decoded to the original URL.

## 代码

Approach 1: Using Simple Counter

public class Codec {
Map<Integer, String> map = new HashMap<>();
int i = 0;
// Encodes a URL to a shortened URL.
public String encode(String longUrl) {
map.put(i, longUrl);
return "http://tinyurl.com" + i++;
}
// Decodes a shortened URL to its original URL.
public String decode(String shortUrl) {
String url = shortUrl.replace("http://tinyurl.com/", "");
return map.get(Integer.parseInt(url));
}
}
// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.decode(codec.encode(url));
Approach #2 Variable-Length Encoding
class Codec {
String chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
HashMap<String, String> map = new HashMap<>();
int count = 1;
public String getString() {
int c = count;
StringBuilder sb = new StringBuilder();
while (c > 0) {
c--;
sb.append(chars.charAt(c % 62));
c /= 62;
}
return sb.toString();
}
public String encode(String longUrl) {
String key = getString();
map.put(key, longUrl);
count++;
return "http://tinyurl.com/" + key;
}
public String decode(String shortUrl) {
String url = shortUrl.replace("http://tinyurl.com/", "");
return map.get(url);
}
}
Approach #3 Using Hashcode
class Codec {
Map<Integer, String> map = new HashMap<>();
public String encode(String longUrl) {
map.put(longUrl.hashCode(), longUrl);
return "http://tinyurl.com/" + longUrl.hashCode();
}
public String decode(String shortUrl) {
String url = shortUrl.replace("http://tinyurl.com/", "");
return map.get(Integer.parseInt(url));
}
}
Approach #4 Using random number
class Codec {
Map<Integer, String> map = new HashMap<>();
Random r = new Random();
int key = r.nextInt(Integer.MAX_VALUE);
public String encode(String longUrl) {
while (map.containsKey(key)) {
key = r.nextInt(Integer.MAX_VALUE);
}
map.put(key, longUrl);
return "http://tinyurl.com/" + key;
}
public String decode(String shortUrl) {
String url = shortUrl.replace("http://tinyurl.com/", "");
return map.get(integer.parseInt(url));
}
}
Approach #5 Random fixed-length encoding
public class Codec {
String alphabet = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
HashMap<String, String> map = new HashMap<>();
Random rand = new Random();
String key = getRand();
public String getRand() {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < 6; i++) {
sb.append(alphabet.charAt(rand.nextInt(62)));
}
return sb.toString();
}
public String encode(String longUrl) {
while (map.containsKey(key)) {
key = getRand();
}
map.put(key, longUrl);
return "http://tinyurl.com/" + key;
}
public String decode(String shortUrl) {
return map.get(shortUrl.replace("http://tinyurl.com/", ""));
}
}