LeetCode 271. Encode and Decode Strings（字符串编解码）

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本文介绍了一种用于网络传输的字符串编解码算法，该算法能够将字符串数组编码为单一字符串，并能将其解码回原始的字符串数组。该算法通过记录每个字符串的长度及其内容来实现编解码过程。

原题网址：https://leetcode.com/problems/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.

思路：把字符串数组按照长度+内容的格式进行编解码。

public class Codec {

    // Encodes a list of strings to a single string.
    public String encode(List<String> strs) {
        char[] lenstr = new char[4];
        StringBuilder sb = new StringBuilder();
        for(String str: strs) {
            int len = str.length();
            for(int j=3; j>=0; j--) {
                lenstr[j] = (char)(len & 0b11111111);
                len >>= 8;
            }
            sb.append(new String(lenstr));
            sb.append(str);
        }
        return sb.toString();
    }

    // Decodes a single string to a list of strings.
    public List<String> decode(String s) {
        List<String> decoded = new ArrayList<>();
        int pos = 0;
        while (pos < s.length()) {
            int len = 0;
            for(int i=0; i<4; i++) len = (len<<8) + s.charAt(pos++);
            decoded.add(s.substring(pos, pos+len));
            pos += len;
        }
        return decoded;
    }
}

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