90 lines
2.7 KiB
Java
90 lines
2.7 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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import edu.princeton.cs.introcs.StdRandom;
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/*************************************************************************
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* Compilation: javac Knuth.java
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* Execution: java Knuth < list.txt
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* Dependencies: StdIn.java StdOut.java
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* Data files: http://algs4.cs.princeton.edu/11model/cards.txt
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*
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* Reads in a list of strings and prints them in random order.
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* The Knuth (or Fisher-Yates) shuffling algorithm guarantees
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* to rearrange the elements in uniformly random order, under
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* the assumption that Math.random() generates independent and
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* uniformly distributed numbers between 0 and 1.
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*
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* % more cards.txt
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* 2C 3C 4C 5C 6C 7C 8C 9C 10C JC QC KC AC
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* 2D 3D 4D 5D 6D 7D 8D 9D 10D JD QD KD AD
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* 2H 3H 4H 5H 6H 7H 8H 9H 10H JH QH KH AH
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* 2S 3S 4S 5S 6S 7S 8S 9S 10S JS QS KS AS
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*
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* % java Knuth < cards.txt
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* 6H
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* 9C
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* 8H
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* 7C
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* JS
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* ...
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* KH
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*
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*************************************************************************/
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/**
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* The Knuth class provides a client for reading in a
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* sequence of strings and shuffling them using the Knuth (or Fisher-Yates)
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* shuffling algorithm. This algorithm guarantees to rearrange the
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* elements in uniformly random order, under
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* the assumption that Math.random() generates independent and
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* uniformly distributed numbers between 0 and 1.
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*
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* For additional documentation, see <a href="http://algs4.cs.princeton.edu/11model">Section 1.1</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 Knuth {
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// this class should not be instantiated
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private Knuth() { }
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/**
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* Rearranges an array of objects in uniformly random order
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* (under the assumption that Math.random() generates independent
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* and uniformly distributed numbers between 0 and 1).
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* @param a the array to be shuffled
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* @see StdRandom
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*/
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public static void shuffle(Object[] a) {
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int N = a.length;
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for (int i = 0; i < N; i++) {
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// choose index uniformly in [i, N-1]
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int r = i + (int) (Math.random() * (N - i));
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Object swap = a[r];
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a[r] = a[i];
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a[i] = swap;
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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, shuffles
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* them, and prints out the results.
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*/
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public static void main(String[] args) {
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// read in the data
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String[] a = StdIn.readAllStrings();
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// shuffle the array
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Knuth.shuffle(a);
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// print results.
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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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