课后作业2

Posted 2020-08-14 木小舟

动手动脑：

1.java类中不用static还能如何调用函数

方法调用：“类名.方法”

如果此函数是动态的，那么只有在调用的时候才会被主动加载一次，之后释放内存。方法调用：必须先实例化出来一个类，之后再通过实例化类名+方法的形式调用。

2.观察以下代码的不同之处

表示方法为静态，在其他类中可以用类名去调用这个方法。

课后作业：

1.求组合数源程序：

1）递归求组合数：

import java.util.Scanner;
 
public class Czuhe {
    public static void main(String[] args)
    {
         
        System.out.print("请输入N：");
        @SuppressWarnings("resource")
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        System.out.print("请输入k：");
        @SuppressWarnings("resource")
        Scanner scan=new Scanner(System.in);
        int K=scan.nextInt();
        System.out.println(Cal(N,K));
    }
    public static int Cal(int N,int K)
    {
         if(K == 0 || N == 0) 
            { 
                return 1; 
            } 
               
            if(N < K) 
            { 
                return 0; 
            } 
               
            if(N == K) 
            { 
                return 1; 
            } 
               
            return Cal(N-1,K) + Cal(N-1,K-1);
    }
}

（2）利用杨辉三角求组合数：

import java.util.Scanner;
@SuppressWarnings("unused")
public class Czuhe {
    public static void main(String[] args)
    {
         
        System.out.print("请输入N：");
        @SuppressWarnings("resource")
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        System.out.print("请输入k：");
        @SuppressWarnings("resource")
        Scanner scan=new Scanner(System.in);
        int K=scan.nextInt();
        System.out.println(Cal(N,K));
    }
    public static int Cal(int N,int K)
    {
         if(K == 0 || N == 0) 
            { 
                return 1; 
            } 
             int c=0;int a=1;
         int s=Math.min(K, N-K);
         for(int i=1;i<=s;i++)
         {
             c=a*(N-i+1)/(i);
             a=c;
         }
               
            return c;
             
    }
}

（3）使用组合数公式计算：

import java.util.Scanner;
@SuppressWarnings("unused")
public class Czuhe {
    public static void main(String[] args) 
    {
        
        System.out.print("请输入N：");
        @SuppressWarnings("resource")
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        System.out.print("请输入k：");
        @SuppressWarnings("resource")
        Scanner scan=new Scanner(System.in);
        int K=scan.nextInt();
        System.out.println(jiecheng(N)/(jiecheng(K)*jiecheng(N-K)));
    }
    public static int jiecheng(int N)
    {
        int s=1;
         if(N == 1)  
            {  
                return 1;  
            }  
        
         else 
             s=jiecheng(N-1)*N  ; 
         return s; 
            
    }
}

2.回文数程序：

import java.util.Scanner;
@SuppressWarnings("unused")
public class HuiWen 
{
    int n=100;
    public static void main(String[] args) 
    {
        System.out.print("请输入字符串：");
        @SuppressWarnings("resource")
        Scanner sc=new Scanner(System.in);
        String N=sc.nextLine();
        if(fun(N)==1)
             System.out.print("是回文字符串！");
        else 
             System.out.print("不是回文字符串！");
    }
    
    
    public static  int fun(  String str)
    {
          int len=str.length();
          
        {  
            if (len == 0 || len == 1)  
                return    1;  
            char first=str.charAt(0);
            char last=str.charAt(len-1);
            if ( first!= last)  
                return    0;  
            return fun(str.substring(1,len-1));  
        }  
    }

}

3.线性同余法生成随机数

import java.util.Date;  
import java.util.concurrent.atomic.AtomicLong;  
  
public class Random {  
      
    private final AtomicLong seed;  
    private final static long multiplier = 0x5DEECE66DL;  
    private final static long addend = 0xBL;  
    private final static long mask = (1L << 48) - 1;  
    private static volatile long seedUniquifier = 8682522807148012L;  
      
    public void srandSeed(long t){  
        this.seed.set(t);  
    }  
      
    public Random(){  
         this(++seedUniquifier + System.nanoTime());  
         System.out.println(seed.get());  
    }  
      
    public Random(long seed) {  
        this.seed = new AtomicLong(0L);  
        srandSeed(seed);  
    }  
      
    int random(int bits){  
        long oldseed = seed.get();  
        long nextseed = (oldseed * multiplier + addend) & mask;  
        return (int)(nextseed >>> (48 - bits));  
    }  
      
    public static void main(String[] args) {  
        Random r = new Random();  
        r.srandSeed(new Date().getTime());  
        System.out.println(r.random(32));  
    }  
}

4.汉诺塔程序

import java.util.Scanner;
 
public class TowersOfHanoi {
 
        public static void solveTowers( int disks, int sourcePeg,
              int destinationPeg, int tempPeg )
           {
               
              if ( disks == 1 )
              {
                 System.out.printf( "\\n%d --> %d", sourcePeg, destinationPeg );
                 return;
              }
 
              
               
              solveTowers( disks - 1, sourcePeg, tempPeg, destinationPeg );
 
               
              System.out.printf( "\\n%d --> %d", sourcePeg, destinationPeg );
 
              
              solveTowers( disks - 1, tempPeg, destinationPeg, sourcePeg );
           }
 
           public static void main( String[] args )
           {
               System.out.print("请输入要移动的盘子数：");
                @SuppressWarnings("resource")
                Scanner sc=new Scanner(System.in);
                @SuppressWarnings("unused")
                int  N=sc.nextInt();
                solveTowers( N, 1, 2, 3 );
                 
           }
         
}