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[LeetCode] 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.

字符串的编码与解码。

请你设计一个算法，可以将一个字符串列表编码成为一个字符串。这个编码后的字符串是可以通过网络进行高效传送的，并且可以在接收端被解码回原来的字符串列表。

思路如下，编码的时候，可以编成这样的格式：stringLength + "/" + string

这样解码的时候，可以通过找到第一个"/"的方式确定每个string的长度，也可以通过这个"/"的位置确定每个string的起始位置，哪怕string本身有"/"。

时间O(n)

空间O(n)

Java实现

 1 public class Codec {
 2 
 3     // Encodes a list of strings to a single string.
 4     public String encode(List<String> strs) {
 5         StringBuilder sb = new StringBuilder();
 6         for (String str : strs) {
 7             // length + '/' + string
 8             sb.append(str.length()).append('/').append(str);
 9         }
10         return sb.toString();
11     }
12 
13     // Decodes a single string to a list of strings.
14     public List<String> decode(String s) {
15         List<String> res = new ArrayList<>();
16         int i = 0;
17         while (i < s.length()) {
18             int slash = s.indexOf('/', i);
19             int size = Integer.valueOf(s.substring(i, slash));
20             res.add(s.substring(slash + 1, slash + 1 + size));
21             i = slash + 1 + size;
22         }
23         return res;
24     }
25 }
26 
27 // Your Codec object will be instantiated and called as such:
28 // Codec codec = new Codec();
29 // codec.decode(codec.encode(strs));

JavaScript实现

 1 /**
 2  * Encodes a list of strings to a single string.
 3  *
 4  * @param {string[]} strs
 5  * @return {string}
 6  */
 7 var encode = function (strs) {
 8     let sb = [];
 9     for (let str of strs) {
10         sb.push(str.length);
11         sb.push('/');
12         sb.push(str);
13     }
14     return sb.join('');
15 };
16 
17 /**
18  * Decodes a single string to a list of strings.
19  *
20  * @param {string} s
21  * @return {string[]}
22  */
23 var decode = function (s) {
24     let res = [];
25     let i = 0;
26     while (i < s.length) {
27         let slash = s.indexOf('/', i);
28         let len = parseInt(s.substring(i, slash));
29         let str = s.substring(slash + 1, slash + 1 + len);
30         res.push(str);
31         i = slash + 1 + len;
32     }
33     return res;
34 };
35 
36 /**
37  * Your functions will be called as such:
38  * decode(encode(strs));
39  */