Question

嘿伙计们，我正在阅读Java编程入门书和其中一个练习：

经验洗牌检查。跑计算实验检查我们的洗牌代码就像标榜。写一个程序需要命令行的ShuffleTest 参数M和N，N个shuffles 一个初始化的大小为M的数组在每次洗牌之前使用[i] = i，并且打印M-by-M表，使得行i 给出了我结束的次数在所有j的位置j。所有条目在数组中应该接近N / M.

现在，这段代码只输出一个零块......

public class ShuffleTest2 {
  public static void main(String[] args) {
    int M = Integer.parseInt(args[0]);
    int N = Integer.parseInt(args[1]); 
    int [] deck = new int [M];

    for (int i = 0; i < M; ++i)
      deck [i] = i;

    int [][] a = new int [M][M];

    for (int i = 0; i < M; i++) {
      for (int j = 0; j < M; j++) {
        a[i][j] = 0 ;

        for(int n = 0; n < N; n++) {
          int r = i + (int)(Math.random() * (M-i));
          int t = deck[r];
          deck[r] = deck[i];
          deck[i] = t;

          for (int b = 0; b < N; b++)
          {
            for (int c = 0; c < M; c++)
              System.out.print(" " + a[b][c]);
            System.out.println();
          }
        }
      }
    }
  }
}

我做错了什么？：（

由于

Answer 1

所以a就像历史？就像你现在一样，它总是像你初始化一样填充零，你永远不会分配给它！在“shuffling”for循环之后，你需要设置

A[i][POSITION] = CARD_VALUE

意思是在第i次洗牌后，卡CARD_VALUE处于POSITION位置。我不想给你所有的细节，但是它将需要另一个for循环，并且用于打印的嵌套for循环需要独立于任何其他循环，在其他所有循环完成时发生。

看起来你有一些关于你需要仔细查看的for循环的事情。手动或使用调试器跟踪程序流程，您会注意到需要移动其中一些大括号和代码块。

- 尝试一下 -

public class ShuffleTest2 {

  public static void main(String[] args) {
    int M = Integer.parseInt(args[0]);
    int N = Integer.parseInt(args[1]); 
    int [] deck = new int [M];

    int [][] a = new int [M][M]; 

    for (int i = 0; i < M; i++) {  //initialize a to all zeroes
      for (int j = 0; j < M; j++) {
        a[i][j] = 0 ; 
      }
    }

    for(int i = 0; i < N; i++)   //puts the deck in order, shuffles it, and records. N times
    {
        for (int j = 0; j < M; j++)  //order the deck
          deck[j] = j;

        for(int j = 0; j < M; j++) {       //shuffle the deck (same as yours except counter name)
          int r = j + (int)(Math.random() * (M-j));
          int t = deck[r];
          deck[r] = deck[j];
          deck[j] = t;
        }

       for(int j = 0; j < M; j++)   //record status of this deck as described
       {
           int card_at_j = deck[j];  //value of card in position j
           a[card_at_j][j]++;        //tally that card_at_j occured in position j
       }
    }  //big loop ended

    for (int b = 0; b < M; b++)  //print loop.  a is MxM, so limit of N was wrong.
    {
        for (int c = 0; c < M; c++)
        {
           System.out.print(" " + a[b][c]);
           System.out.println();
        }
    }  //print loop ended
  }  //main() ended
 } //class ended

我如何用java中的二维数组完成这个问题？

1 个答案: