EncodeAndDecodeStrings271.java

/**
 * 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.
 */

public class EncodeAndDecodeStrings271 {
    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<>();
            int i=0;
            while (i < s.length()) {
                int j = i;
                while (s.charAt(j) != '|') j++;
                String sizeString = s.substring(i, j);
                int size = Integer.valueOf(sizeString);
                String str = s.substring(j+1, j+size+1);
                list.add(str);
                i += sizeString.length() + 1 + size;
            }
            return list;
        }
    }

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

}