Encode and Decode Strings

Design an algorithm to encode a list of strings to a string. The encoded string is then sent over the network and is decoded back to the original list of strings.

Machine 1 (sender) has the function:

public String encode(String[] strs) {
  // ... your code
  return encoded_string;
}

Machine 2 (receiver) has the function:

public String[] decode(String s) {
  //... your code
  return strs;
}

So Machine 1 does:

String encoded_string = encode(strs);

and Machine 2 does:

String[] strs2 = decode(encoded_string);

strs2 in Machine 2 should be the same as strs in Machine 1.

Implement the encode and decode methods.

Note

The string may contain any possible characters out of 256 valid ascii characters. Your algorithm should be generalized enough to work on any possible characters.

Do not use class member / global / static variables to store states. Your encode and decode algorithms should be stateless.

Do not rely on any library method such as eval or serialize methods. You should implement your own encode/decode algorithm.

Think

• In theoretic way, there should be nothing can do separation for Strings
• So just make the encode as adding the length of word and "#" before the word
• Decode function should be carefully designed

Solution

public class EncodeDecodeString {
    public String encode(List<String> strs) {
        StringBuilder sb = new StringBuilder();
        for (String str : strs) {
            sb.append(str.length());
            sb.append("#");
            sb.append(str);
        }

        return sb.toString();
    }

    public List<String> decode(String str) {
        List<String> list = new ArrayList<>();
        int strlen = 0;
        for (int i = 0; i < str.length(); i++) {
            char cur = str.charAt(i);
            if (cur == '#' && strlen > 0) {
                StringBuilder sb = new StringBuilder();
                while (strlen > 0 && i < str.length()) {
                    sb.append(str.charAt(++i));
                    strlen--;
                }
                list.add(sb.toString());
            } else
                strlen = strlen * 10 + (cur - '0');
        }
        return list;
    }
}