271. Encode and Decode Strings ---------- M~~~

 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.

A:

就是每个string前面加一个长度， 然后用特殊符号隔离。这样，即使input含有特殊符号也不怕

class Codec {
public:

    // Encodes a list of strings to a single string.
    string encode(vector<string>& strs) {
        // record letnght of each word, followed by a "#", then, no matter what's contained in word, we are good to go.
        string res="";
        for(auto & s: strs){
            res+=to_string(s.length())+"#"+s;
        }
        return res;        
    }

    // Decodes a single string to a list of strings.
    vector<string> decode(string s) {
        vector<string> res;
        int start = 0, end = 0;
        while(end<s.length()){
            while(end<s.length() && s[end]!='#'){
                end++;
            }
            // for sure, we would see a '#'
            int len = stoi(s.substr(start, end-start));
            res.push_back(s.substr(end+1,len));
            start = end+1+len;
            end = start;
        }
        return res;
    }
};

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