> For the complete documentation index, see [llms.txt](https://maksimdan.gitbook.io/interview-practice-problems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://maksimdan.gitbook.io/interview-practice-problems/leetcode_sessions/271-encode-and-decode-strings.md).

# 271 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.

A somewhat trival, but accepted solution

```cpp
    // Encodes a list of strings to a single string.
    string encode(vector<string>& strs) {
        string encoded = "";
        for (string s : strs) {
            for (char c : s) {
                encoded += c + 1;
            }
            encoded += ' ';
        }
        return encoded;
    }

    // Decodes a single string to a list of strings.
    vector<string> decode(string s) {
        vector<string> decoded;
        string temp = "";
        for (char c : s) {
            if (c == ' ') {
                decoded.push_back(temp);
                temp.clear();
            }
            else temp += c - 1;
        }
        return decoded;
    }
```

Congrats on the find

```cpp
vector<int> encode(string &s, vector<int> &key) 
{
    if (key.size() < s.length()) {
        cout << "invalid key length" << endl;
        exit(0);
    }

    vector<int> encoded;
    int iter = 0;

    for (char c : s) {
        if (iter % 2 == 0) 
            encoded.push_back((int)c * key[iter++]);
        else encoded.push_back((int)c + key[iter++]);
    }
    return encoded;
}

string decode(vector<int> &encoded, vector<int> &key)
{
    string decoded = "";
    int iter = 0;

    for (int i : encoded) {
        if (iter % 2 == 0)
            decoded += (char)(i / key[iter++]);
        else decoded += (char)(i - key[iter++]);
    }

    return decoded;
}

string concate_input(int argc, char **argv)
{    
    string final_con = "";
    for (int i = 1; i < argc; i++) {
        final_con += argv[i];
    }
    return final_con;
}

int main(int argc, char **argv)
{
    if (argc < 2) {
        cout << "expected one or more arguments" << endl;
        exit(0);
    }

    // support 20 characters
    vector<int> key =  { 
        42,    282,    -264,    -287,    12,
        280,    145,    192,    274,    -56,
        -43,    -279,    -297,    125,    10,
        176,    279,    -234,    -243,    -184 };

    string msg = concate_input(argc, argv);
    cout << msg << endl;
    vector<int> encoded = encode(msg, key);

    cout << "encoded: ";
    for (int i: encoded) cout << i << ' ';
    cout << endl;

    string decoded = decode(encoded, key);
    cout << "decoded: " << decoded << endl;
}
```