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