StringCoder - Part B¶

Part b. Write the StringCoder method encodeString. A string is encoded by determining the substrings in the master string that can be combined to generate the given string. The encoding starts with a string part that matches the beginning of the word, followed by a string part that matches the beginning of the rest of the word, and so on. The string parts are returned in an array list in the order in which they appear in word. The helper method findPart must be used to choose matching string parts in the master string.

Try and Solve It¶

Complete method encodeString below.

The code below has a main method for testing your method.

import java.util.*;

class StringPart
{
   private int start;
   private int len;

public StringPart(int theStart, int theLen)
   {
      // initialise instance variables
      start = theStart;
      len=theLen;
   }

public StringPart()
   {
      start = 0;
      len = 0;
   }

public int getStart()
   {
      return start;
   }

public int getLength()
   {
     return len;
   }

public String toString()
   {
     return "(" + getStart() + ", " + getLength() + ")";
   }
}

public class StringCoder
{

private String masterString;

/**
     * Constructor for objects of class StringCoder
     */
   public StringCoder()
   {
      masterString="sixtyzipperswerequicklypickedfromthewovenjutebag";
   }

public StringCoder(String master)
   {
      masterString=master;
   }

/** @param parts an ArrayList of string parts that are
     * valid in the master string
     * Precondition: parts.size() > 0
     * @return the string obtained by concatenating the parts
     * of the master string
     */
   public String decodeString(ArrayList<StringPart> parts)
   {
      String s = "";
      for (StringPart part : parts)
          s = s + masterString.substring(part.getStart(), part.getStart() + part.getLength());
      return s;
   }

private StringPart findPart(String str)
   {
      int start=0;
      int length=0;
      for (int len=1; len<=str.length(); len++)
      {
         int found=masterString.indexOf(str.substring(0,len));
         if (found!=-1)
         {
            start=found;
            length=len;
         }
       }
       return new StringPart(start, length);
   }

/** @param word the string to be encoded
     * Precondition: all of the characters in word
     * appear in the master string;
     * word.length() > 0
     * @return an ArrayList of string parts of the master
     * string that can be combined
     * to create word
     */
   public ArrayList<StringPart> encodeString(String word)
   {
      //*** Write this method for part b! ***

}

public static void main(String[] args)
   {
      ArrayList<StringPart> overeager = new ArrayList<StringPart>();
      overeager.add(new StringPart(37,3));
      overeager.add(new StringPart(14,2));
      overeager.add(new StringPart(46,2));
      overeager.add(new StringPart(9,2));
      System.out.println("overeager should be encoded as " + overeager);
      StringCoder key=new StringCoder();
      System.out.println("Testing part b overeager is encoded as " + key.encodeString("overeager"));
   }

}

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