Below is the syntax highlighted version of QuickBentleyMcIlroy.java.
/****************************************************************************** * Compilation: javac QuickBentleyMcIlroy.java * Execution: java QuickBentleyMcIlroy < input.txt * Dependencies: StdOut.java StdIn.java * Data files: https://algs4.cs.princeton.edu/23quicksort/tiny.txt * https://algs4.cs.princeton.edu/23quicksort/words3.txt * * Uses the Bentley-McIlroy 3-way partitioning scheme, * chooses the partitioning element using Tukey's ninther, * and cuts off to insertion sort. * * Reference: Engineering a Sort Function by Jon L. Bentley * and M. Douglas McIlroy. Software-Practice and Experience, * Vol. 23 (11), 1249-1265 (November 1993). * ******************************************************************************/ package edu.princeton.cs.algs4; /** * The {@code QuickBentleyMcIlroy} class provides static methods for sorting * an array using an optimized version of quicksort (using Bentley-McIlroy * 3-way partitioning, Tukey's ninther, and cutoff to insertion sort). * <p> * For additional documentation, see * <a href="https://algs4.cs.princeton.edu/23quicksort">Section 2.3</a> * of <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne. * * @author Robert Sedgewick * @author Kevin Wayne */ public class QuickBentleyMcIlroy { // cutoff to insertion sort, must be >= 1 private static final int INSERTION_SORT_CUTOFF = 8; // cutoff to median-of-3 partitioning private static final int MEDIAN_OF_3_CUTOFF = 40; // This class should not be instantiated. private QuickBentleyMcIlroy() { } /** * Rearranges the array in ascending order, using the natural order. * @param a the array to be sorted */ public static void sort(Comparable[] a) { sort(a, 0, a.length - 1); } private static void sort(Comparable[] a, int lo, int hi) { int n = hi - lo + 1; // cutoff to insertion sort if (n <= INSERTION_SORT_CUTOFF) { insertionSort(a, lo, hi); return; } // use median-of-3 as partitioning element else if (n <= MEDIAN_OF_3_CUTOFF) { int m = median3(a, lo, lo + n/2, hi); exch(a, m, lo); } // use Tukey ninther as partitioning element else { int eps = n/8; int mid = lo + n/2; int m1 = median3(a, lo, lo + eps, lo + eps + eps); int m2 = median3(a, mid - eps, mid, mid + eps); int m3 = median3(a, hi - eps - eps, hi - eps, hi); int ninther = median3(a, m1, m2, m3); exch(a, ninther, lo); } // Bentley-McIlroy 3-way partitioning int i = lo, j = hi+1; int p = lo, q = hi+1; Comparable v = a[lo]; while (true) { while (less(a[++i], v)) if (i == hi) break; while (less(v, a[--j])) if (j == lo) break; // pointers cross if (i == j && eq(a[i], v)) exch(a, ++p, i); if (i >= j) break; exch(a, i, j); if (eq(a[i], v)) exch(a, ++p, i); if (eq(a[j], v)) exch(a, --q, j); } i = j + 1; for (int k = lo; k <= p; k++) exch(a, k, j--); for (int k = hi; k >= q; k--) exch(a, k, i++); sort(a, lo, j); sort(a, i, hi); } // sort from a[lo] to a[hi] using insertion sort private static void insertionSort(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); } // return the index of the median element among a[i], a[j], and a[k] private static int median3(Comparable[] a, int i, int j, int k) { return (less(a[i], a[j]) ? (less(a[j], a[k]) ? j : less(a[i], a[k]) ? k : i) : (less(a[k], a[j]) ? j : less(a[k], a[i]) ? k : i)); } /*************************************************************************** * Helper sorting functions. ***************************************************************************/ // is v < w ? private static boolean less(Comparable v, Comparable w) { if (v == w) return false; // optimization when reference equal return v.compareTo(w) < 0; } // does v == w ? private static boolean eq(Comparable v, Comparable w) { if (v == w) return true; // optimization when reference equal 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; quicksorts them * (using an optimized version of quicksort); * 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(); QuickBentleyMcIlroy.sort(a); assert isSorted(a); show(a); } } /****************************************************************************** * Copyright 2002-2022, 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. ******************************************************************************/