128 lines
3.8 KiB
Java
128 lines
3.8 KiB
Java
|
|
|
|
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);
|
|
}
|
|
|
|
}
|