public class Codec {

public static final char[] ALPHABETS = {

'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',

'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p',

'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',

'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',

'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '-', '_'

};

public static final int BASE = 64;

public static final Random rand = new Random();

private Map<String, String> lookup = new HashMap<>();

// Encodes a URL to a shortened URL.

public String encode(String longUrl) {

StringBuilder str = new StringBuilder();

for (int i=0; i<7; i++) {

str.append(ALPHABETS[rand.nextInt(BASE)]);

}

String key = str.toString();

lookup.put(key, longUrl);

return key;

}

// Decodes a shortened URL to its original URL.

public String decode(String shortUrl) {

return lookup.get(shortUrl);

}

}

public class Codec2 {

private char[] BASE62 = new char[]{

'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',

'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',

'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',

'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',

'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'

};

Map<String, String> map = new HashMap<>();

int id = 0;

// Encodes a URL to a shortened URL.

public String encode(String longUrl) {

StringBuilder sb = new StringBuilder();

int n = id;

while (n != 0) {

sb.append(BASE62[n % 26]);

n /= 62;

}

sb.append(BASE62[n % 26]);

String key = sb.toString();

if (!map.containsKey(key)) {

map.put(key, longUrl);

id++;

}

return key;

}

// Decodes a shortened URL to its original URL.

public String decode(String shortUrl) {

return map.get(shortUrl);

}

}

// Your Codec object will be instantiated and called as such:

// Codec codec = new Codec();

// codec.decode(codec.encode(url));