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Heap2.java
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103 lines (92 loc) · 3.11 KB
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package heap;
/******************************************************************************
* Compilation: javac Heap.java
* Execution: java Heap < input.txt
* Dependencies: StdOut.java StdIn.java
* Data files: https://algs4.cs.princeton.edu/24pq/tiny.txt
* https://algs4.cs.princeton.edu/24pq/words3.txt
*
* Sorts a sequence of strings from standard input using heapsort.
*
* % more tiny.txt
* S O R T E X A M P L E
*
* % java Heap < 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 Heap < words3.txt
* all bad bed bug dad ... yes yet zoo [ one string per line ]
*
******************************************************************************/
import java.util.Scanner;
/**
* The {@code Heap} class provides a static methods for heapsorting
* an array.
* <p>
* For additional documentation, see <a href="https://algs4.cs.princeton.edu/24pq">Section 2.4</a> of
* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class Heap2 {
// This class should not be instantiated.
private Heap2() { }
/**
* Rearranges the array in ascending order, using the natural order.
* @param pq the array to be sorted
*/
public static void sort(Comparable[] pq) {
int n = pq.length;
for (int k = n/2; k >= 1; k--)
sink(pq, k, n);
while (n > 1) {
exch(pq, 1, n--);
sink(pq, 1, n);
}
}
/***************************************************************************
* Helper functions to restore the heap invariant.
***************************************************************************/
private static void sink(Comparable[] pq, int k, int n) {
while (2*k <= n) {
int j = 2*k;
if (j < n && less(pq, j, j+1)) j++;
if (!less(pq, k, j)) break;
exch(pq, k, j);
k = j;
}
}
/***************************************************************************
* Helper functions for comparisons and swaps.
* Indices are "off-by-one" to support 1-based indexing.
***************************************************************************/
private static boolean less(Comparable[] pq, int i, int j) {
return pq[i-1].compareTo(pq[j-1]) < 0;
}
private static void exch(Object[] pq, int i, int j) {
Object swap = pq[i-1];
pq[i-1] = pq[j-1];
pq[j-1] = swap;
}
// print array to standard output
private static void show(Comparable[] a) {
for (int i = 0; i < a.length; i++) {
System.out.println(a[i]);
}
}
/**
* Reads in a sequence of strings from standard input; heapsorts them;
* and prints them to standard output in ascending order.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
// String[] a = Scanner.readAllStrings();
// Heap2.sort(a);
// show(a);
}
}