0271-encode-and-decode-strings.cpp

/*
    Design algorithm to encode/decode: list of strings <-> string

    Encode/decode w/ non-ASCII delimiter: {len of str, "#", str}

    Time: O(n)
    Space: O(1)
*/

class Codec {
public:

    // Encodes a list of strings to a single string.
    string encode(vector<string>& strs) {
        string result = "";
        
        for (int i = 0; i < strs.size(); i++) {
            string str = strs[i];
            result += to_string(str.size()) + "#" + str;
        }
        
        return result;
    }

    // Decodes a single string to a list of strings.
    vector<string> decode(string s) {
        vector<string> result;
        
        int i = 0;
        while (i < s.size()) {
            int j = i;
            while (s[j] != '#') {
                j++;
            }
            int length = stoi(s.substr(i, j - i));
            string str = s.substr(j + 1, length);
            result.push_back(str);
            i = j + 1 + length;
        }
        
        return result;
    }
private:
};

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