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.

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?

Solution:

public class Codec {

    // Encodes a list of strings to a single string.
    public String encode(List<String> strs) { // ["Hello","World"]
        StringBuilder sb = new StringBuilder();
        for (String s : strs){
            sb.append(s);
            sb.append("π");
        }
        // "HelloπWorld"

        return sb.toString();
    }

    // Decodes a single string to a list of strings.
    public List<String> decode(String s) { //"HelloπWorld"
        String[] sb = s.split("π", -1); // ""
        // ["Hello", "World", ""]     // [""]
        return Arrays.asList(sb).subList(0, sb.length -1);
        // [0, 2] // 0

    }
}

// TC: O(n)

// SC: O(k)

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

public class Codec {

    // Encodes a list of strings to a single string.
    public String encode(List<String> strs) {
        StringBuilder sb = new StringBuilder();
        for (String s : strs){
            sb.append(s);
            sb.append("π"); // out of 256 of ASCII
        }

        return sb.toString();

    }

    // Decodes a single string to a list of strings.
    public List<String> decode(String s) {//"HelloπWorldπGoodbyeπ"
        String[] sb = s.split("π", -1); // -1 为了空“” 
        // ["Hello", "World", "Goodbye", ""]
        return Arrays.asList(sb).subList(0, sb.length - 1);
        // [0, 3) -> [0, 2]

    }

}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.decode(codec.encode(strs)); 
// TC: O(n)
// SC: O(k)

??? 题看不懂?

好像看懂了点 "encode a list of strings to a string. "

熟悉Arrays的API 以及String的API, 加强练习不然老容易忘记