0271-encode-and-decode-strings

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Description

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?

Solution(Python)

class Codec:
    def encode(self, strs: List[str]) -> str:
        """Encodes a list of strings to a single string.
        """
        return ChunkedTransferencoding().encode(strs)

    def decode(self, s: str) -> List[str]:
        """Decodes a single string to a list of strings.
        """
        return  ChunkedTransferencoding().decode(s)


class DelimiterCodec(Codec):
    def encode(self, strs: List[str]) -> str:
        """Encodes a list of strings to a single string.
        """
        return "¶".join(strs)

    def decode(self, s: str) -> List[str]:
        """Decodes a single string to a list of strings.
        """
        return s.split("¶")


class EscapedDelimiterCodec(Codec):
    def encode(self, strs: List[str]) -> str:
        """Encodes a list of strings to a single string.
        """
        encoded_string = ''
        # Iterate over each string in the input list
        for s in strs:
            # Replace each occurrence of '/' with '//'
            # This is our way of "escaping" the slash character
            # Then add our delimiter '/:' to the end
            encoded_string += s.replace('/', '//') + '/:'
        
        return encoded_string

    def decode(self, s: str) -> List[str]:
        """Decodes a single string to a list of strings.
        """
        decoded_strings = []
        cur_string = ''
        i = 0
        while i < len(s):
            if s[i:i+2] == '/:':
                decoded_strings.append(cur_string)
                cur_string = ''
                i +=2
            elif s[i:i+2] == '//':
                cur_string += '/'
                i +=2
            else:
                cur_string += s[i]
                i += 1
        return decoded_strings


class ChunkedTransferencoding(Codec):
    def encode(self, strs: List[str]) -> str:
        """Encodes a list of strings to a single string.
        """
        # 5/:Hello5/:World11/:/:Example/:
        # append length /: + string
        encoded_string = ''
        for s in strs:
            # Append the length, the delimiter, and the string itself.
            encoded_string += str(len(s)) + '/:' + s
        return encoded_string



    def decode(self, s: str) -> List[str]:
        """Decodes a single string to a list of strings.
        """
        #  5/:Hello5/:World11/:/:Example/:
        # i < n
        #   read until next /:
        #   curl_len = i
        #   get cur_word form = i + 2 -> i + 2 + cur_len
        decoded_strings = []
        i = 0
        while i < len(s):
            # Find the delimiter.
            delim = s.find('/:', i)
            # Get the length, which is before the delimiter.
            length = int(s[i:delim])
            # Get the string, which is of 'length' length after the delimiter.
            str_ = s[delim+2 : delim+2+length]
            # Add the string to the list.
            decoded_strings.append(str_)
            # Move the index to the start of the next length.
            i = delim + 2 + length
        return decoded_strings

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

Dry Run