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:

string encode(vector<string> strs) {
  // ... your code
  return encoded_string;
}

Machine 2 (receiver) has the function:

vector<string> decode(string s) {
  //... your code
  return strs;
}

So Machine 1 does:

string encoded_string = encode(strs);

and Machine 2 does:

vector<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.

Solution:

public class Codec {
  // Encodes a list of strings to a single string.
  public String encode(List<String> strs) {
    StringBuilder sb = new StringBuilder();
    for(String s : strs) {
      sb.append(s.length()).append('/').append(s);
    }
    return sb.toString();
  }
  // Decodes a single string to a list of strings.
  public List<String> decode(String s) {
    List<String> ret = new ArrayList<String>();
    int i = 0;
    while(i < s.length()) {
      int slash = s.indexOf('/', i);
      int size = Integer.valueOf(s.substring(i, slash));
      ret.add(s.substring(slash + 1, slash + size + 1));
      i = slash + size + 1;
    }
    return ret;
  }
}
// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.decode(codec.encode(strs));