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.

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

Use a special sequence to denote the end of a string, and escape the sequence. Be careful of empty string and empty input as they’re different!

class Codec:

    def encode(self, strs):
        """Encodes a list of strings to a single string.

        :type strs: List[str]
        :rtype: str
        """
        if len(strs) == 0:
            return ""
        else:
            return "//".join([s.replace("/", "#/#") for s in strs]) + "//"


    def decode(self, s):
        """Decodes a single string to a list of strings.

        :type s: str
        :rtype: List[str]
        """
        if len(s) == 0:
            return []
        return [seg.replace("#/#", "/") for seg in s.split("//")][:-1]


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