[LeetCode271]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.

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編碼:把一大堆string編成一個string
譯碼:把那一個string變回一大堆

對於一個string,它的長度和起始位置可以確定整個string。比如我們有: dog, cat, bird, tiger.要encode成爲一個string我們可以利用特殊符號表示起始位置:[email protected]@[email protected]@tiger。
當然string長度可以大於9。

Decode:每次先找數字(長度)再找@,從@之後開始長度爲len的substr就是一個string。

class Codec {
public:

    // Encodes a list of strings to a single string.
    string encode(vector<string>& strs) {
        string encoded = "";
        for(auto s : strs){
            int len = s.size();
            encoded += to_string(len) + "@" + s;
        }
        return encoded;
    }

    // Decodes a single string to a list of strings.
    vector<string> decode(string s) {
        vector<string> res;
        int head = 0;
        while(head < s.size()){
            int atPos = s.find_first_of('@', head);
            int len = stoi(s.substr(head, atPos - head));
            res.push_back(s.substr(atPos+1, len));
            head = atPos + len + 1;
        }
        return res;
    }
};

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