CC150 20.2

標籤：interview

20.2 Write a method to shuffle a deck of cards. It must be a perfect shuffle - in other words, each 52! permutations of the deck has to be equally likely. Assume that you are given a random number generator which is perfect.

// Randomly generate a int k from 1(inclusive) to n(inclusive).int random(int n);class DeckShuffle(){  // Init a deck with 52 cards.  private int[] init()    // Swap element  private void swap(int[] a, int from, int to)    int[] next()  {      int[] deck = init();        for (int i = 0 ; i < deck.length - 1 ; i ++)    {      int pos = random(52 - i);      swap(deck, pos, i);    }        return deck;  }  }

CC150 20.2