import edu.princeton.cs.introcs.StdIn; import edu.princeton.cs.introcs.StdOut; /************************************************************************* * Compilation: javac Shell.java * Execution: java Shell < 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 shellsort. * * Uses increment sequence proposed by Sedgewick and Incerpi. * The nth element of the sequence is the smallest integer >= 2.5^n * that is relatively prime to all previous terms in the sequence. * For example, incs[4] is 41 because 2.5^4 = 39.0625 and 41 is * the next integer that is relatively prime to 3, 7, and 16. * * % more tiny.txt * S O R T E X A M P L E * * % java Shell < 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 Shell < words3.txt * all bad bed bug dad ... yes yet zoo [ one string per line ] * * *************************************************************************/ /** * The Shell class provides static methods for sorting an * array using Shellsort with Knuth's increment sequence (1, 4, 13, 40, ...). * * For additional documentation, see <a href="http://algs4.cs.princeton.edu/21elementary">Section 2.1</a> of * Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne. * * @author Robert Sedgewick * @author Kevin Wayne */ public class Shell { // This class should not be instantiated. private Shell() { } /** * 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; // 3x+1 increment sequence: 1, 4, 13, 40, 121, 364, 1093, ... int h = 1; while (h < N/3) h = 3*h + 1; while (h >= 1) { // h-sort the array for (int i = h; i < N; i++) { for (int j = i; j >= h && less(a[j], a[j-h]); j -= h) { exch(a, j, j-h); } } assert isHsorted(a, h); h /= 3; } 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; } // is the array h-sorted? private static boolean isHsorted(Comparable[] a, int h) { for (int i = h; i < a.length; i++) if (less(a[i], a[i-h])) 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; Shellsorts them; * and prints them to standard output in ascending order. */ public static void main(String[] args) { String[] a = StdIn.readAllStrings(); Shell.sort(a); show(a); } }