271. 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.

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());
            sb.append("#");
            sb.append(s);
        }

        return sb.toString();

    }

    // Decodes a single string to a list of strings.
    public List<String> decode(String s) {

        List<String> res = new ArrayList<>();
        int k = 0;

        while(k < s.length()){
            int pound = s.indexOf("#", k);
            int size = Integer.parseInt(s.substring(k, pound));
            res.add(s.substring(pound+1, pound+1+size));
            k = pound+1+size;
        }

        return res;

    }
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.decode(codec.encode(strs));