無法在Java中實現quicksort遞歸

Question

我正在為學校做一個項目，我必須測試拼寫檢查實現的二進制搜索與線性搜索的速度。 我們必須使用此特定的SpellCheck。 我的教授為使用遞歸進行binary搜索提供的示例是為int設計的一些單獨的代碼片段，他希望我們使它適用於帶有字符串的此實現。 任何幫助，我們將不勝感激。 SortedWordList是我需要幫助的類。

 import java.util.Scanner;


public class Spellcheck {

    private static WordList listOfWords;// The list of correctly spelled words.


    public static void main(String[] args) {
        long start = System.nanoTime();
        listOfWords = new SortedWordList();
        //listOfWords = new WordList();
        long end = System.nanoTime(); 
        long WL = (end-start);
        //end = 0;
        //start = 0;
        long SW = 0;
        Scanner in = new Scanner(System.in);
        while (true) {  // Get and process one word from the user.
            System.out.println();
            System.out.print("Enter a word to be cheched (press return to end):  ");
            String word = in.nextLine().trim().toLowerCase();
            start = System.nanoTime();
            if (word.length() == 0)
                break;
            if (listOfWords.contains(word)) {
                System.out.println("'" + word + "' is a legal word.");

            }
            else {
                System.out.println("'" + word + "' is not a legal word.");
                System.out.println("If there are similar words, they are shown here:");
                trySubstitute(word);
                tryInsert(word);
                tryDelete(word);
                trySwap(word);
                tryBreak(word);
                end = System.nanoTime();
                SW = (end-start);
            }
            System.out.println();
            System.out.printf("Time to create word list: %,d nanoseconds.%n",(WL));
            System.out.println();
            System.out.printf("Time to test for similar words: %,d nanoseconds.%n",(SW));
            System.out.println();
            System.out.printf("Time to test total: %,d nanoseconds.%n",(SW + WL));
        }

    }

    private static void trySubstitute(String word) {
        for (int i = 0; i < word.length(); i++) {
            String before = word.substring(0, i);
            String after = word.substring(i+1);
            for (char ch = 'a'; ch < 'z'; ch++) {
                String newword = before + ch + after;
                if (listOfWords.contains(newword))
                    System.out.println("   " + newword);
            }
        }
    }

    private static void tryInsert(String word) {
        for (int i = 0; i <= word.length(); i++) {
            String before = word.substring(0,i);
            String after = word.substring(i);
            for (char ch = 'a'; ch < 'z'; ch++) {
                String newword = before + ch + after;
                if (listOfWords.contains(newword))
                    System.out.println("   " + newword);
            }
        }
    }

    private static void tryDelete(String word) {
        for (int i = 0; i < word.length(); i++) {
            String before = word.substring(0, i);
            String after = word.substring(i+1);
            String newword = before + after;
            if (listOfWords.contains(newword))
                System.out.println("   " + newword);
        }
    }


    private static void trySwap(String word) {
        for (int i = 0; i < word.length() - 1; i++) {
            String before = word.substring(0, i);
            char a = word.charAt(i);
            char b = word.charAt(i+1);
            String after = word.substring(i+2);
            String newword = before + b + a + after;
            if (listOfWords.contains(newword)) 
                System.out.println("   " + newword);

        }
    }

    private static void tryBreak(String word) {
        for (int i = 1; i < word.length() - 1; i++) {
            String before = word.substring(0, i);
            String after = word.substring(i);
            if (listOfWords.contains(before) && listOfWords.contains(after))
                System.out.println("   " + before + " " + after);
        }       
    }

} // end class Spellcheck
`

import java.util.ArrayList;
import java.util.Scanner;
import java.net.URL;


public class WordList {

   protected final String[] words;  // the list of words

   public WordList() {
      try {
         URL listLocation = WordList.class.getClassLoader().getResource("unsorted_words.txt");
         Scanner in = new Scanner( listLocation.openStream() );
         ArrayList<String> wordList = new ArrayList<String>();
         while (in.hasNextLine())
            wordList.add(in.nextLine());
         words = wordList.toArray(new String[] {});
         in.close();
      }
      catch (Exception e) {
         throw new IllegalStateException("Can't load list of words from file 'unsorted_words.txt'");
      }
   }

   public boolean contains(String lowerCaseWord) {
      for (String s : words) {
         if (s.equals(lowerCaseWord))
            return true;
      }
      return false;
   }

   public int size() {
      return words.length;
   }

   public String get(int index) {
      return words[index];
   }


}

import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Scanner;

public class SortedWordList extends WordList {


    public String [] words;


    public SortedWordList() { 
        URL listLocation = SortedWordList.class.getClassLoader().getResource("unsorted_words.txt");
        Scanner in = null;
        try {
            in = new Scanner( listLocation.openStream() );
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        ArrayList<String> wordList = new ArrayList<String>();
        while (in.hasNextLine())
           wordList.add(in.nextLine());
        words = wordList.toArray(new String[] {});
        in.close();
    }

        //public boolean contains(String lowerCaseWord) {

       //}


    static int binarySearch(String[] A, int loIndex, int hiIndex, String value) {

       if (loIndex > hiIndex) {

          return -1;
       }

       else {

          int middle = (loIndex + hiIndex) / 2;
          if (value == A[middle])
             return middle;
          else if ((A[middle].compareTo(value)) > 0)
             return binarySearch(A, loIndex, middle - 1, value);
          else   // value must be > A[middle]
             return binarySearch(A, middle + 1, hiIndex, value);
       }

    } // end binarySearch()




     static int quicksortStep(String[] A, int lo, int hi) {

        String pivot = A[lo];  // Get the pivot value.



        while (hi > lo) {

           while (hi > lo && ((pivot.compareTo(A[hi])) <= 0)) {

              hi--;
           }

           if (hi == lo)
              break;

           A[lo] = A[hi];
           lo++;

           while (hi > lo && ((pivot.compareTo(A[lo])) >= 0)) {

              lo++;
           }

           if (hi == lo)
              break;

           A[hi] = A[lo];
           hi--;

        } // end while

        A[lo] = pivot;
        return lo;

     }  // end QuicksortStep


     static void quicksort(String[] A, int lo, int hi) {

            if (hi <= lo) {

               return;
            }
            else {

               int pivotPosition = quicksortStep(A, lo, hi);
               quicksort(A, lo, pivotPosition - 1);
               quicksort(A, pivotPosition + 1, hi);
            }
         }


}

Answer 1

首先，您需要在哪里打電話給quicksort？ 只是通過類的SortedWordList名稱進行猜測，在我看來，您需要在SortedWordList的構造函數中調用此quicksort方法。 現在，構造函數似乎正在加載未排序的單詞列表。

如果那不能解決問題，那么我還要再次查看SortedWordList類中的quicksortStep方法。 這個quicksortStep方法基本上是分區方法。 （例如，請參見https://www.programcreek.com/2012/11/quicksort-array-in-java/ ）。 我將嘗試在quicksortStep方法中遵循與上面鏈接中的分區方法相同的代碼結構，然后將其修改為字符串，直到類似：

public static int partition(String[] arr, int start, int end){
    String pivot = arr[end];

    for(int i=start; i<end; i++){
        if((arr[i].compareTo(pivot)) < 0){
            String temp= arr[start];
            arr[start]=arr[i];
            arr[i]=temp;
            start++;
        }
    }

    String temp = arr[start];
    arr[start] = pivot;
    arr[end] = temp;

    return start;
}

隨意重命名方法/變量。