271

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;
}

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.

You are not allowed to solve the problem using any serialize methods (such as eval).

 

Example 1:

Input: dummy_input = ["Hello","World"]
Output: ["Hello","World"]
Explanation:
Machine 1:
Codec encoder = new Codec();
String msg = encoder.encode(strs);
Machine 1 ---msg---> Machine 2
Machine 2:
Codec decoder = new Codec();
String[] strs = decoder.decode(msg);

Example 2:

Input: dummy_input = [""]
Output: [""]

 

Constraints:

• 1 <= strs.length <= 200
• 0 <= strs[i].length <= 200
• strs[i] contains any possible characters out of 256 valid ASCII characters.

 

Follow up: Could you write a generalized algorithm to work on any possible set of characters?

Companies: Facebook, Amazon, Square

Related Topics:
Array, String, Design

Similar Questions:

• Count and Say (Medium)
• Serialize and Deserialize Binary Tree (Hard)
• String Compression (Medium)
• Count Binary Substrings (Easy)

Solution 1.

We use $x as a separator. To avoid confusing the $x in the original string as a separator, we escape $ sign using $ sign, so ab$xcd is escaped to be ab$$xcd.

// OJ: https://leetcode.com/problems/encode-and-decode-strings/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Codec {
public:
    string encode(vector<string>& strs) {
        string ans;
        for (string &str : strs) {
            for (char c : str) {
                if (c == '$') ans.push_back(c);
                ans.push_back(c);
            }
            ans.push_back('$');
            ans.push_back('x');
        }
        return ans;
    }
    vector<string> decode(string s) {
        vector<string> ans;
        int i = 0, N = s.size();
        while (i < N) {
            string str;
            for (; i < N; ++i) {
                if (s[i] != '$') str.push_back(s[i]);
                else if (i + 1 < N && s[i + 1] == '$') str.push_back(s[i++]);
                else {
                    i += 2;
                    break;
                }
            }
            ans.push_back(str);
        }
        return ans;
    }
};