271. Encode and Decode Strings (Medium)

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 1:

这道题让我们给字符加码再解码，先有码再无码，然后题目中并没有限制我们加码的方法，那么我们的方法只要能成功的把有码变成无码就行了，具体变换方法我们自己设计。由于我们需要把一个字符串集变成一个字符串，然后把这个字符串再还原成原来的字符串集，最开始我想能不能在每一个字符串中间加个空格把它们连起来，然后再按空格来隔开，但是这种方法的问题是原来的一个字符串中如果含有空格，那么还原的时候就会被分隔成两个字符串，所以我们必须还要加上长度的信息，我们的加码方法是长度+"/"+字符串，比如对于"a","ab","abc"，我们就变成"1/a2/ab3/abc"，那么我们解码的时候就有规律可寻，先寻找"/"，然后之前的就是要取出的字符个数，从“/"后取出相应个数即可，以此类推直至没有"/"了，这样我们就得到高清无码的字符串集了，参见代码如下：

class Codec {
public:

    // Encodes a list of strings to a single string.
    string encode(vector<string>& strs) {
        string res;
        for (auto str:strs) {
            res += to_string(str.size())+' '+str;
        }
        return res;
    }

    // Decodes a single string to a list of strings.
    vector<string> decode(string s) {
        vector<string> res;
        int i = 0;
        while (i < s.size()) {
            int len = 0;
            while (s[i] != ' ') {
                len = len*10+s[i++]-'0';
            }
            res.push_back(s.substr(i+1, len));
            i += len+1;
        }
        return res;
    }
};

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