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## Problem

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) {
return encoded_string;
}


Machine 2 (receiver) has the function:

vector<string> decode(string s) {
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: [""]


## Code

public class Codec {
// Encodes a list of strings to a single string.
public String encode(List<String> strs) {
StringBuilder sb = new StringBuilder();
for (String str : strs){
sb.append(str.length() + "/" + str);
}

return sb.toString();
}

// Decodes a single string to a list of strings.
public List<String> decode(String s) {
List<String> res = new ArrayList<>();
int index = 0;

while (index < s.length()){
int sep = s.indexOf("/", index);
int len = Integer.valueOf(s.substring(index, sep));
String curr = s.substring(sep + 1, sep + 1 + len);
index = sep + 1 + len;
}

return res;
}
}

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

class Codec:
def encode(self, strs: [str]) -> str:
"""Encodes a list of strings to a single string.
"""
if len(strs) == 0:
return chr(258)
# 找一个不是256 ascii的作为分隔符
return chr(257).join(x for x in strs)

def decode(self, s: str) -> [str]:
"""Decodes a single string to a list of strings.
"""
if s == chr(258):
return []

return s.split(chr(257))

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