stringselectionsort.java

java编程代码

import java.util.ArrayList;

/**
 Class for sorting an ArrayList of Strings lexicographically
 (approximately alphabetically).
*/
 public class StringSelectionSort
 {
    /**
     Sorts the ArrayList a so that a.get(0), a.get(1), . . ., 
     a.get(a.size( ) - 1) are in lexicographic order.
    */
     public static void sort(ArrayList<String> a)
     {
        int index, indexOfNextSmallest;
        for (index = 0; index < a.size( ) - 1; index++)
        {//Place the correct value in position index:
            indexOfNextSmallest = 
                            indexOfSmallest(index, a);
            interchange(index,indexOfNextSmallest, a);
            //a.get(0), a.get(1),...,a.get(index)
            //are sorted. The rest of the
            //elements are in the remaining positions.
        }
     }
     
    /**
      Precondition: i and j are legal indices for the ArrayList a.
      Postcondition: The values of a.get(i) and
      a.get(j) have been interchanged.
     */
     private static void interchange(
                                int i, int j, ArrayList<String> a)
     {
        String temp;
        temp = a.get(i);
        a.set(i, a.get(j));
        a.set(j, temp);
     }
     
    /**
     Returns the index of the lexicographically first value among
     a.get(startIndex), a.get(startIndex+1),...,a.get(a.size( ) - 1)
    */
    private static int indexOfSmallest(
                                 int startIndex, ArrayList<String> a)
    {
        String min = a.get(startIndex);
        int indexOfMin = startIndex;
        int index;
        for (index = startIndex + 1; index < a.size( ); index++)
        if ((a.get(index)).compareTo(min) < 0)
        {
            min = a.get(index);
            indexOfMin = index;
        }
        return indexOfMin;
    }
}