Quick3string.java
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/******************************************************************************
* Compilation: javac Quick3string.java
* Execution: java Quick3string < input.txt
* Dependencies: StdIn.java StdOut.java
* Data files: http://algs4.cs.princeton.edu/51radix/words3.txt
* http://algs4.cs.princeton.edu/51radix/shells.txt
*
* Reads string from standard input and 3-way string quicksort them.
*
* % java Quick3string < shell.txt
* are
* by
* sea
* seashells
* seashells
* sells
* sells
* she
* she
* shells
* shore
* surely
* the
* the
*
*
******************************************************************************/
package edu.princeton.cs.algs4;
/**
* The {@code Quick3string} class provides static methods for sorting an
* array of strings using 3-way radix quicksort.
* <p>
* For additional documentation,
* see <a href="http://algs4.cs.princeton.edu/51radix">Section 5.1</a> of
* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class Quick3string {
private static final int CUTOFF = 15; // cutoff to insertion sort
// do not instantiate
private Quick3string() { }
/**
* Rearranges the array of strings in ascending order.
*
* @param a the array to be sorted
*/
public static void sort(String[] a) {
StdRandom.shuffle(a);
sort(a, 0, a.length-1, 0);
assert isSorted(a);
}
// return the dth character of s, -1 if d = length of s
private static int charAt(String s, int d) {
assert d >= 0 && d <= s.length();
if (d == s.length()) return -1;
return s.charAt(d);
}
// 3-way string quicksort a[lo..hi] starting at dth character
private static void sort(String[] a, int lo, int hi, int d) {
// cutoff to insertion sort for small subarrays
if (hi <= lo + CUTOFF) {
insertion(a, lo, hi, d);
return;
}
int lt = lo, gt = hi;
int v = charAt(a[lo], d);
int i = lo + 1;
while (i <= gt) {
int t = charAt(a[i], d);
if (t < v) exch(a, lt++, i++);
else if (t > v) exch(a, i, gt--);
else i++;
}
// a[lo..lt-1] < v = a[lt..gt] < a[gt+1..hi].
sort(a, lo, lt-1, d);
if (v >= 0) sort(a, lt, gt, d+1);
sort(a, gt+1, hi, d);
}
// sort from a[lo] to a[hi], starting at the dth character
private static void insertion(String[] a, int lo, int hi, int d) {
for (int i = lo; i <= hi; i++)
for (int j = i; j > lo && less(a[j], a[j-1], d); j--)
exch(a, j, j-1);
}
// exchange a[i] and a[j]
private static void exch(String[] a, int i, int j) {
String temp = a[i];
a[i] = a[j];
a[j] = temp;
}
// is v less than w, starting at character d
// DEPRECATED BECAUSE OF SLOW SUBSTRING EXTRACTION IN JAVA 7
// private static boolean less(String v, String w, int d) {
// assert v.substring(0, d).equals(w.substring(0, d));
// return v.substring(d).compareTo(w.substring(d)) < 0;
// }
// is v less than w, starting at character d
private static boolean less(String v, String w, int d) {
assert v.substring(0, d).equals(w.substring(0, d));
for (int i = d; i < Math.min(v.length(), w.length()); i++) {
if (v.charAt(i) < w.charAt(i)) return true;
if (v.charAt(i) > w.charAt(i)) return false;
}
return v.length() < w.length();
}
// is the array sorted
private static boolean isSorted(String[] a) {
for (int i = 1; i < a.length; i++)
if (a[i].compareTo(a[i-1]) < 0) return false;
return true;
}
/**
* Reads in a sequence of fixed-length strings from standard input;
* 3-way radix quicksorts them;
* and prints them to standard output in ascending order.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
// read in the strings from standard input
String[] a = StdIn.readAllStrings();
int n = a.length;
// sort the strings
sort(a);
// print the results
for (int i = 0; i < n; i++)
StdOut.println(a[i]);
}
}
/******************************************************************************
* 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.
******************************************************************************/