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.

encode的时候，给每个string后面加“|”，decode的时候根据“|”进行分解拼接。这里split函数需要有点注意：

From Document: If n is non-positive then the pattern will be applied as many times as possible and the array can have any length. If n is zero then the pattern will be applied as many times as possible, the array can have any length, and trailing empty strings will be discarded.

代码如下：

public class Codec {    // Encodes a list of strings to a single string.    public String encode(List<String> strs) {        StringBuilder sb = new StringBuilder();        for (String str: strs) {            sb.append(str.length()).append("|").append(str);        }        return sb.toString();    }    // Decodes a single string to a list of strings.    public List<String> decode(String s) {        List<String> list = new ArrayList<String>();        int index = s.indexOf("|");        while (index != -1) {            int len = Integer.valueOf(s.substring(0, index));            list.add(s.substring(index + 1, index + 1 + len));            s = s.substring(index + 1 + len);            index = s.indexOf("|");        }        return list;    }}// Your Codec object will be instantiated and called as such:// Codec codec = new Codec();// codec.decode(codec.encode(strs));

另一种top solution方法：

public String encode(List<String> strs) {    StringBuffer out = new StringBuffer();    for (String s : strs)        out.append(s.replace("#", "##")).append(" # ");    return out.toString();}public List<String> decode(String s) {    List strs = new ArrayList();    String[] array = s.split(" # ", -1);    for (int i=0; i<array.length-1; ++i)        strs.add(array[i].replace("##", "#"));    return strs;}