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.

Solution:

class Codec:
    def encode(self, strings):
        """
        Encodes a list of strings to a single string.
        :type strings: List[str]
        :rtype: str
        """
        result = []
        for string in strings:
            result.append('{}/'.format(len(string)))
            result.append(string)
        return ''.join(result)

    def decode(self, s):
        """
        Decodes a single string to a list of strings.
        :type s: str
        :rtype: List[str]
        """
        result = []
        idx = 0
        while idx < len(s):
            slash = s.find('/', idx)
            size = int(s[idx: slash])
            idx = slash + 1 + size
            result.append(s[slash + 1: idx])
        return result

Lessons:

• Use length information to encode string.