Insertion.java


Below is the syntax highlighted version of Insertion.java.


/******************************************************************************
 *  Compilation:  javac Insertion.java
 *  Execution:    java Insertion < input.txt
 *  Dependencies: StdOut.java StdIn.java
 *  Data files:   http://algs4.cs.princeton.edu/21elementary/tiny.txt
 *                http://algs4.cs.princeton.edu/21elementary/words3.txt
 *  
 *  Sorts a sequence of strings from standard input using insertion sort.
 *
 *  % more tiny.txt
 *  S O R T E X A M P L E
 *
 *  % java Insertion < 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 Insertion < words3.txt
 *  all bad bed bug dad ... yes yet zoo   [ one string per line ]
 *
 ******************************************************************************/

package edu.princeton.cs.algs4;

import java.util.Comparator;

/**
 *  The {@code Insertion} class provides static methods for sorting an
 *  array using insertion sort.
 *  <p>
 *  This implementation makes ~ 1/2 n^2 compares and exchanges in
 *  the worst case, so it is not suitable for sorting large arbitrary arrays.
 *  More precisely, the number of exchanges is exactly equal to the number
 *  of inversions. So, for example, it sorts a partially-sorted array
 *  in linear time.
 *  <p>
 *  The sorting algorithm is stable and uses O(1) extra memory.
 *  <p>
 *  See <a href="http://algs4.cs.princeton.edu/21elementary/InsertionPedantic.java.html">InsertionPedantic.java</a>
 *  for a version that eliminates the compiler warning.
 *  <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 Insertion {

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

    /**
     * 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;
        for (int i = 0; i < n; i++) {
            for (int j = i; j > 0 && less(a[j], a[j-1]); j--) {
                exch(a, j, j-1);
            }
            assert isSorted(a, 0, i);
        }
        assert isSorted(a);
    }

    /**
     * Rearranges the subarray a[lo..hi) in ascending order, using the natural order.
     * @param a the array to be sorted
     * @param lo left endpoint (inclusive)
     * @param hi right endpoint (exclusive)
     */
    public static void sort(Comparable[] a, int lo, int hi) {
        for (int i = lo; i < hi; i++) {
            for (int j = i; j > lo && less(a[j], a[j-1]); j--) {
                exch(a, j, j-1);
            }
        }
        assert isSorted(a, lo, hi);
    }

    /**
     * Rearranges the array in ascending order, using a comparator.
     * @param a the array
     * @param comparator the comparator specifying the order
     */
    public static void sort(Object[] a, Comparator comparator) {
        int n = a.length;
        for (int i = 0; i < n; i++) {
            for (int j = i; j > 0 && less(a[j], a[j-1], comparator); j--) {
                exch(a, j, j-1);
            }
            assert isSorted(a, 0, i, comparator);
        }
        assert isSorted(a, comparator);
    }

    /**
     * Rearranges the subarray a[lo..hi) in ascending order, using a comparator.
     * @param a the array
     * @param lo left endpoint (inclusive)
     * @param hi right endpoint (exclusive)
     * @param comparator the comparator specifying the order
     */
    public static void sort(Object[] a, int lo, int hi, Comparator comparator) {
        for (int i = lo; i < hi; i++) {
            for (int j = i; j > lo && less(a[j], a[j-1], comparator); j--) {
                exch(a, j, j-1);
            }
        }
        assert isSorted(a, lo, hi, comparator);
    }


    // return a permutation that gives the elements in a[] in ascending order
    // do not change the original array a[]
    /**
     * Returns a permutation that gives the elements in the array in ascending order.
     * @param a the array
     * @return a permutation {@code p[]} such that {@code a[p[0]]}, {@code a[p[1]]},
     *    ..., {@code a[p[n-1]]} are in ascending order
     */
    public static int[] indexSort(Comparable[] a) {
        int n = a.length;
        int[] index = new int[n];
        for (int i = 0; i < n; i++)
            index[i] = i;

        for (int i = 0; i < n; i++)
            for (int j = i; j > 0 && less(a[index[j]], a[index[j-1]]); j--)
                exch(index, j, j-1);

        return index;
    }

   /***************************************************************************
    *  Helper sorting functions.
    ***************************************************************************/
    
    // is v < w ?
    private static boolean less(Comparable v, Comparable w) {
        return v.compareTo(w) < 0;
    }

    // is v < w ?
    private static boolean less(Object v, Object w, Comparator comparator) {
        return comparator.compare(v, 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;
    }

    // exchange a[i] and a[j]  (for indirect sort)
    private static void exch(int[] a, int i, int j) {
        int swap = a[i];
        a[i] = a[j];
        a[j] = swap;
    }

   /***************************************************************************
    *  Check if array is sorted - useful for debugging.
    ***************************************************************************/
    private static boolean isSorted(Comparable[] a) {
        return isSorted(a, 0, a.length);
    }

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

    private static boolean isSorted(Object[] a, Comparator comparator) {
        return isSorted(a, 0, a.length, comparator);
    }

    // is the array a[lo..hi) sorted
    private static boolean isSorted(Object[] a, int lo, int hi, Comparator comparator) {
        for (int i = lo+1; i < hi; i++)
            if (less(a[i], a[i-1], comparator)) 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();
        Insertion.sort(a);
        show(a);
    }
}

/******************************************************************************
 *  Copyright 2002-2016, Robert Sedgewick and Kevin Wayne.
 *
 *  This file is part of algs4.jar, which accompanies the textbook
 *
 *      Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
 *      Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
 *      http://algs4.cs.princeton.edu
 *
 *
 *  algs4.jar is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  algs4.jar is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with algs4.jar.  If not, see http://www.gnu.org/licenses.
 ******************************************************************************/


Last updated: Sun Apr 16 20:48:46 EDT 2017.