InsertionX.java


Below is the syntax highlighted version of InsertionX.java from §2.1 Elementary Sorts.


/******************************************************************************
 *  Compilation:  javac InsertionX.java
 *  Execution:    java InsertionX < input.txt
 *  Dependencies: StdOut.java StdIn.java
 *  Data files:   http://algs4.cs.princeton.edu/21sort/tiny.txt
 *                http://algs4.cs.princeton.edu/21sort/words3.txt
 *  
 *  Sorts a sequence of strings from standard input using an optimized
 *  version of insertion sort that uses half exchanges instead of 
 *  full exchanges to reduce data movement..
 *
 *  % more tiny.txt
 *  S O R T E X A M P L E
 *
 *  % java InsertionX < tiny.txt
 *  A E E L M O P R S T X                 [ one string per line ]
 *
 *  % more words3.txt
 *  bed bug dad yes zoo ... all bad yet
 *
 *  % java InsertionX < words3.txt
 *  all bad bed bug dad ... yes yet zoo   [ one string per line ]
 *
 ******************************************************************************/
/**
 *  The {@code InsertionX} class provides static methods for sorting
 *  an array using an optimized version of insertion sort (with half exchanges
 *  and a sentinel).
 *  <p>
 *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/21elementary">Section 2.1</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */

public class InsertionX {

    // This class should not be instantiated.
    private InsertionX() { }

    /**
     * Rearranges the array in ascending order, using the natural order.
     * @param a the array to be sorted
     */
    public static void sort(Comparable[] a) {
        int n = a.length;

        // put smallest element in position to serve as sentinel
        int exchanges = 0;
        for (int i = n-1; i > 0; i--) {
            if (less(a[i], a[i-1])) {
                exch(a, i, i-1);
                exchanges++;
            }
        }
        if (exchanges == 0) return;


        // insertion sort with half-exchanges
        for (int i = 2; i < n; i++) {
            Comparable v = a[i];
            int j = i;
            while (less(v, a[j-1])) {
                a[j] = a[j-1];
                j--;
            }
            a[j] = v;
        }

        assert isSorted(a);
    }


   /***************************************************************************
    *  Helper sorting functions.
    ***************************************************************************/
    
    // is v < w ?
    private static boolean less(Comparable v, Comparable w) {
        return v.compareTo(w) < 0;
    }
        
    // exchange a[i] and a[j]
    private static void exch(Object[] a, int i, int j) {
        Object swap = a[i];
        a[i] = a[j];
        a[j] = swap;
    }


   /***************************************************************************
    *  Check if array is sorted - useful for debugging.
    ***************************************************************************/
    private static boolean isSorted(Comparable[] a) {
        for (int i = 1; i < a.length; i++)
            if (less(a[i], a[i-1])) return false;
        return true;
    }

    // print array to standard output
    private static void show(Comparable[] a) {
        for (int i = 0; i < a.length; i++) {
            StdOut.println(a[i]);
        }
    }

    /**
     * Reads in a sequence of strings from standard input; insertion sorts them;
     * and prints them to standard output in ascending order.
     *
     * @param args the command-line arguments
     */
    public static void main(String[] args) {
        String[] a = StdIn.readAllStrings();
        InsertionX.sort(a);
        show(a);
    }

}


Copyright © 2002–2016, Robert Sedgewick and Kevin Wayne.
Last updated: Tue Aug 30 10:09:18 EDT 2016.