《Java语言程序设计与数据结构》编程练习答案（第六章）（三）

英文名：Introduction to Java Programming and Data Structures, Comprehensive Version, 11th Edition

6.27

public class book {
       public static void main(String[] args)    {
           int count=0;        int base=0;        int dick = 2;        while(count<100)        {
               if(isPrime(dick)&&!isPalindrome(dick)&&isPrime(reverse(dick)))            {
                   System.out.print(dick+" ");                count++;            }            if(count%10==0&&count!=base) {
                   System.out.print('\n');                base+=10;            }            dick++;        }    }    public static boolean isPrime(int n)    {
           for(int i=2;i<=n/2;i++)        {
               if(n%i==0)                return false;        }        return true;    }    public static boolean isPalindrome(int n)    {
           String ass = Integer.toString(n);        for(int i=0;i
   
    =0;i--)            dick+=ass.charAt(i);        return Integer.parseInt(dick);    }}

6.28

public class book {
       public static void main(String[] args)    {
           System.out.println("p           2^p-1");        System.out.println("-----------------");        for(int i=2;i<=31;i++)        {
               int jb = (int)Math.pow(2,i)-1;            if(isPrime(jb))                System.out.printf("%d\t\t%-2d\n",i,jb);        }    }    public static boolean isPrime(int n)    {
           for(int i=2;i<=n/2;i++)        {
               if(n%i==0)                return false;        }        return true;    }}

6.29

public class book {
       public static void main(String[] args)    {
           for(int i=2;i<=997;i++)        {
               if(isPrime(i)&&isPrime(i+2))                System.out.println("("+i+", "+(i+2)+")");        }    }    public static boolean isPrime(int n)    {
           for(int i=2;i<=n/2;i++)        {
               if(n%i==0)                return false;        }        return true;    }}

6.30

public class book {
       public static void main(String[] args)    {
           dice();    }    public static boolean dice()    {
           int d1 = (int)(Math.random()*6)+1;        int d2 = (int)(Math.random()*6)+1;        int sum = d1+d2;        if(sum==2||sum==3||sum==12) {
               System.out.printf("You rolled %d+%d = %d\nYou lose\n",d1,d2,sum);            return false;        }        else if(sum==7||sum==11) {
               System.out.printf("You rolled %d+%d = %d\nYou win\n",d1,d2,sum);            return true;        }        else        {
               System.out.printf("You rolled %d+%d = %d\n",d1,d2,sum);            System.out.println("point is "+sum);            int old = sum;            do{
                   int j1 = (int)(Math.random()*6)+1;                int j2 = (int)(Math.random()*6)+1;                sum=j1+j2;                System.out.printf("You rolled %d+%d = %d\n",j1,j2,sum);                if(sum==7) {
                       System.out.println("You lose");                    return false;                }                else if(sum!=old)                    System.out.println("point is "+sum);            }while(sum!=old);            System.out.println("You win");            return true;        }    }}

6.31

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter a credit card number: ");        String ass = input.next();        if(isValid(ass))            System.out.println(ass+" is valid");        else            System.out.println(ass+" is invalid");    }    public static boolean isValid(String number)    {
           if(number.length()<13||number.length()>16)            return false;        else        {
               return (sumOfDoubleEvenPlace(number)+sumOfOddPlace(number))%10==0;        }    }    public static int sumOfDoubleEvenPlace(String number)    {
           int sum=0;        for(int i=number.length()-2;i>=0;i-=2)            sum+=getDigit(2*(number.charAt(i)-'0'));        return sum;    }    public static int getDigit(int number)    {
           if(number<10)            return number;        else            return number/10+number%10;    }    public static int sumOfOddPlace(String number)    {
           int sum=0;        for(int i=number.length()-1;i>=0;i-=2)            sum+=(int)(number.charAt(i)-'0');        return sum;    }    public static boolean prefixMatched(String number)    {
           char c1=number.charAt(0);        char c2=number.charAt(1);        return c1 == '4' || c1 == '5' || c1 == '6' || (c1 == '3') && (c2 == 7);    }}

6.32

public class book {
       public static void main(String[] args)    {
           int winCount=0;        for(int i=0;i<10000;i++)        {
               if(dice())                winCount++;        }        System.out.println("You won "+winCount+" times");    }    public static boolean dice()    {
           int d1 = (int)(Math.random()*6)+1;        int d2 = (int)(Math.random()*6)+1;        int sum = d1+d2;        if(sum==2||sum==3||sum==12) {
               return false;        }        else if(sum==7||sum==11) {
               return true;        }        else        {
               int old = sum;            do{
                   int j1 = (int)(Math.random()*6)+1;                int j2 = (int)(Math.random()*6)+1;                sum=j1+j2;                if(sum==7) {
                       return false;                }            }while(sum!=old);            return true;        }    }}

6.33

🐰🌶

6.34

见3.21

6.35

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter the side: ");        double ass = input.nextDouble();        System.out.println("The area of the pentagon is "+area(ass));    }    public static double area(double side)    {
           return 5*side*side/(4*Math.tan(3.141592654/5));    }}

6.36

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter thr number of sides: ");        int n=input.nextInt();        System.out.print("Enter the side: ");        double ass = input.nextDouble();        System.out.println("The area of the polygon is "+area(n,ass));    }    public static double area(int n,double side)    {
           return n*side*side/(4*Math.tan(3.141592654/n));    }}

6.37

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter the number : ");        int n=input.nextInt();        System.out.print("Enter the width : ");        int w = input.nextInt();        System.out.println("The format of the number is "+format(n,w));    }    public static String format(int number,int width)    {
           String ass = Integer.toString(number);        int len = ass.length();        if(len>=width)            return ass;        else        {
               String dick="";            for(int i=1;i<=width-len;i++)                dick+='0';            return dick+ass;        }    }}

6.38

public class book {
       public static void main(String[] args)    {
           for(int i=1;i<=100;i++)        {
               System.out.print(getRandomUpperCaseLetter()+" ");            if(i%10==0)                System.out.print('\n');        }        for(int i=1;i<=100;i++)        {
               System.out.print(getRandomDigitCharacter()+" ");            if(i%10==0)                System.out.print('\n');        }    }    public static char getRandomCharacter(char ch1,char ch2)    {
           return (char)(ch1+Math.random()*(ch2-ch1+1));    }    public static char getRandomUpperCaseLetter()    {
           return getRandomCharacter('A','Z');    }    public static char getRandomDigitCharacter()    {
           return getRandomCharacter('0','9');    }}

6.39

import java.util.Scanner;public class book {
       public static void main(String[] args)    {
           Scanner input = new Scanner(System.in);        System.out.print("Enter three points for p0,p1,p2: ");        double x0 = input.nextDouble();        double y0 = input.nextDouble();        double x1 = input.nextDouble();        double y1 = input.nextDouble();        double x2 = input.nextDouble();        double y2 = input.nextDouble();        if(leftOfTheLine(x0,y0,x1,y1,x2,y2))            System.out.println("On the left");        else if(onTheLineSegment(x0,y0,x1,y1,x2,y2))            System.out.println("On the line segment");        else if(onTheSameLine(x0,y0,x1,y1,x2,y2))            System.out.println("On the same line");        else            System.out.println("On the right");    }    public static boolean leftOfTheLine(double x0,double y0,                                        double x1,double y1,double x2,double y2)    {
           return (x1-x0)*(y2-y0)-(x2-x0)*(y1-y0)>0;    }    public static boolean onTheSameLine(double x0,double y0,                                         double x1,double y1,double x2,double y2)    {
           return (x1-x0)*(y2-y0)-(x2-x0)*(y1-y0)==0;    }    public static boolean onTheLineSegment(double x0,double y0,                                        double x1,double y1,double x2,double y2)    {
           return (x1-x0)*(y2-y0)-(x2-x0)*(y1-y0)==0&&x2>=x0&&x2<=x1;    }}