StringEncoderDecoder.java

package com.interview.string;

import java.util.ArrayList;
import java.util.List;

/**
 * Date 04/06/2016
 * @author Tushar Roy
 *
 * 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.
 *
 * Reference
 * https://leetcode.com/problems/encode-and-decode-strings/
 */
public class StringEncoderDecoder {

    // Encodes a list of strings to a single string.
    public String encode(List<String> strs) {
        StringBuffer buff = new StringBuffer();
        for (String str : strs) {
            String size = toFixedLength(str.length());
            buff.append(size);
            buff.append(str);
        }
        return buff.toString();
    }

    private String toFixedLength(int len) {
        StringBuffer buff = new StringBuffer();
        for (int i = 0; i < 4; i++) {
            char b1 = (char) len;
            buff.append(b1);
            len = len >> 8;
        }
        return buff.toString();
    }

    private int toSize(String str) {
        int val = 0;
        for (int i = str.length() - 1; i > 0; i--) {
            val += str.charAt(i);
            val = val << 8;
        }
        val += str.charAt(0);
        return val;
    }

    // Decodes a single string to a list of strings.
    public List<String> decode(String s) {
        List<String> result = new ArrayList<>();
        while (s.length() != 0) {
            int size = toSize(s.substring(0, 4));
            result.add(s.substring(4, size + 4));
            s = s.substring(size + 4);
        }
        return result;
    }
}