Leetcode 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.

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.

public class Codec {

    // Encodes a list of strings to a single string.
    public string encode(IList<string> strs) {
        var sb = new StringBuilder();
        
        foreach (var s in strs)
        {
            sb.Append(s.Length);
            sb.Append('#');
            sb.Append(s);
        }
        
        return sb.ToString();
    }

    // Decodes a single string to a list of strings.
    public IList<string> decode(string s) {
        var result = new List<string>();
        if (s == null || s.Length == 0) return result;
        
        int i = 0, j = 0;
        
        while (j < s.Length)
        {
            if (s[j] != '#')
            {
                j++;
            }
            else
            {
                var len = Int32.Parse(s.Substring(i, j - i));
                if (len == 0)
                {
                    result.Add("");
                }
                else
                {
                    result.Add(s.Substring(j + 1, len));
                }
                
                j += len + 1;
                i = j;
            }
        }
        
        return result;
    }
}

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