Encode and Decode Strings

Source

• leetcode: 271

esign 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.

Java

public String encode(List<String> strs){
  StringBuilder sb = new StringBuilder();
  for(String s: strs){
    sb.append(s.length()).append('/').append(s);
  }
  return sb.toString();
}

public List<String> decode(String s){
  List<String> res = new ArrayList<string>();

  int i=0;
  while(i<s.length()){
    int slash = s.indexOf('/', i);
    int size = Integer.valueOf(s.substring(i, slash));
    res.add(s.substring(slash+1, slash+size+1));
    i = slash+size+1;
  }
  return res;
}