Question

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.

You are not allowed to solve the problem using any serialize methods (such as eval).

Example 1:

Input: dummy_input = ["Hello","World"]
Output: ["Hello","World"]
Explanation:
Machine 1:
Codec encoder = new Codec();
String msg = encoder.encode(strs);
Machine 1 ---msg---> Machine 2

Machine 2:
Codec decoder = new Codec();
String[] strs = decoder.decode(msg);

Example 2:

Input: dummy_input = [""]
Output: [""]

Constraints:

• 1 <= strs.length <= 200
• 0 <= strs[i].length <= 200
• strs[i] contains any possible characters out of 256 valid ASCII characters.

Follow up: Could you write a generalized algorithm to work on any possible set of characters?

Algorithm

1. If we are not allowed to use any built in method and ASCII, then we can use a non-ascii character;
2. Or an algorithm provided by others: Chunked Transfer Encoding to allow any characters transferring.
   1. Instead using delimiter, we use a length + a delimiter. In such way each time we decode a string we only focus on current chunk with specific length.

Code1

Use limit parameter to include empty string in the split result when decoding.

public class Codec {

    // Encodes a list of strings to a single string.
    public String encode(List<String> strs) {
        StringBuilder sb = new StringBuilder();
        for (String str : strs) {
            sb.append(str);
            sb.append("ÿ");
        }
        return sb.toString();
    }

    // Decodes a single string to a list of strings.
    public List<String> decode(String s) {
        s = s.substring(0, s.length() - 1);
        List<String> res = Arrays.asList(s.split("ÿ", -1));
        
        return res;
    }
}

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

Code2(Chunked Transfer Encoding)

public class Codec {

    // Encodes a list of strings to a single string.
    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();
    }

    // Decodes a single string to a list of strings.
    public List<String> decode(String s) {
        List<String> res = new ArrayList<>();
        int index = 0;

        while (index < s.length()) {
            int indexOfDeli = s.indexOf("#", index);
            int curLen = Integer.parseInt(s.substring(index, indexOfDeli));
            String temp = s.substring(indexOfDeli + 1, indexOfDeli + 1 + curLen);
            res.add(temp);
            index = indexOfDeli + 1 + curLen;
        }
        return res;
    }
    
    
}