001package algs11; 002import stdlib.*; 003/* *********************************************************************** 004 * Compilation: javac Shuffle.java 005 * Execution: java Shuffle < list.txt 006 * Data files: http://algs4.cs.princeton.edu/11model/cards.txt 007 * 008 * Reads in a list of strings and prints them in random order. 009 * The Knuth (or Fisher-Yates) shuffling algorithm guarantees 010 * to rearrange the elements in uniformly random order, under 011 * the assumption that Math.random() generates independent and 012 * uniformly distributed numbers between 0 and 1. 013 * 014 * % more cards.txt 015 * 2C 3C 4C 5C 6C 7C 8C 9C 10C JC QC KC AC 016 * 2D 3D 4D 5D 6D 7D 8D 9D 10D JD QD KD AD 017 * 2H 3H 4H 5H 6H 7H 8H 9H 10H JH QH KH AH 018 * 2S 3S 4S 5S 6S 7S 8S 9S 10S JS QS KS AS 019 * 020 * % java Shuffle < cards.txt 021 * 6H 022 * 9C 023 * 8H 024 * 7C 025 * JS 026 * ... 027 * KH 028 * 029 *************************************************************************/ 030 031public class Shuffle { 032 public static void main(String[] args) { 033 StdIn.fromFile ("data/cards.txt"); 034 035 // read in the data 036 String[] a = StdIn.readAll().split("\\s+"); 037 int N = a.length; 038 039 // shuffle 040 for (int i = 0; i < N; i++) { 041 // int from remainder of deck 042 int r = i + (int) (Math.random() * (N - i)); 043 String swap = a[r]; 044 a[r] = a[i]; 045 a[i] = swap; 046 } 047 048 // print permutation 049 for (int i = 0; i < N; i++) 050 StdOut.println(a[i]); 051 } 052}