[Leetcode] 271. Encode and Decode Strings 解题报告

本文介绍了如何设计一个算法来将字符串列表编码为一个字符串，然后在网络中传输并解码回原始字符串列表。讨论了在两个不同机器上实现的`encode`和`decode`方法，确保解码后的结果与原始列表相同。算法思路包括编码字符串长度以及在长度后添加特殊符号以指示长度字符串的结束。解码过程则与编码相反。该算法避免使用类成员变量、全局变量和静态变量，并不依赖库函数，实现了无状态的编码/解码过程。

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题目：

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：

对于每个字符串，我们首先encode它的长度，但是如果长度大于9，则会有多个解析的可能，所以我们特地在长度之后加一个特殊符号用来表示长度字符串的结束，接着才真正encode字符串。decode的过程和这个刚好相反。这种方法只是一种encode和decode字符串的一种方式，应该还会有其它方式的。

代码：

class Codec {
public:

    // Encodes a list of strings to a single string.
    string encode(vector<string>& strs) {
        string ret;
        for(int i = 0; i < strs.size(); ++i) {
            ret += to_string(strs[i].length());
            ret += "#";
            ret += strs[i];
        }
        return ret;
    }

    // Decodes a single string to a list of strings.
    vector<string> decode(string s) {
        vector<string> ret;
        int start = 0;
        while(start < s.length()) {
            int end = start;
            while(s[end] != '#') {
                end++;
            }
            int length = stoi(s.substr(start, end - start));
            ret.push_back(s.substr(end + 1, length));
            start = end + 1 + length;
        }
        return ret;
    }
};

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