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))