BinaryInsertion.java
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/******************************************************************************
* Compilation: javac BinaryInsertion.java
* Execution: java BinaryInsertion < 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
* binary insertion sort with half exchanges.
*
* % more tiny.txt
* S O R T E X A M P L E
*
* % java BinaryInsertion < 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 BinaryInsertion < words3.txt
* all bad bed bug dad ... yes yet zoo [ one string per line ]
*
******************************************************************************/
package edu.princeton.cs.algs4;
/**
* The {@code BinaryInsertion} class provides a static method for sorting an
* array using an optimized binary insertion sort with half exchanges.
* <p>
* This implementation makes ~ n lg n compares for any array of length n.
* However, in the worst case, the running time is quadratic because the
* number of array accesses can be proportional to n^2 (e.g, if the array
* is reverse sorted). As such, it is not suitable for sorting large
* arrays (unless the number of inversions is small).
* <p>
* The sorting algorithm is stable and uses O(1) extra memory.
* <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 Ivan Pesin
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class BinaryInsertion {
// This class should not be instantiated.
private BinaryInsertion() { }
/**
* 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 = 1; i < n; i++) {
// binary search to determine index j at which to insert a[i]
Comparable v = a[i];
int lo = 0, hi = i;
while (lo < hi) {
int mid = lo + (hi - lo) / 2;
if (less(v, a[mid])) hi = mid;
else lo = mid + 1;
}
// insetion sort with "half exchanges"
// (insert a[i] at index j and shift a[j], ..., a[i-1] to right)
for (int j = i; j > lo; --j)
a[j] = a[j-1];
a[lo] = v;
}
assert isSorted(a);
}
/***************************************************************************
* Helper sorting function.
***************************************************************************/
// is v < w ?
private static boolean less(Comparable v, Comparable w) {
return v.compareTo(w) < 0;
}
/***************************************************************************
* Check if array is sorted - useful for debugging.
***************************************************************************/
private static boolean isSorted(Comparable[] a) {
return isSorted(a, 0, a.length - 1);
}
// is the array sorted from a[lo] to a[hi]
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;
}
// 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();
BinaryInsertion.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.
******************************************************************************/