Java语言程序设计与数据结构(梁勇版) 基础版课后习题第三章

怼烎@ 2022-03-09 08:46 237阅读 0赞

3.1

import java.util.Scanner;
    
    /**
     * 解一元二次方程
     */
    public class T3_1 {
        public static void main(String[] args) {
            Scanner scanner = new Scanner(System.in);
            System.out.print("Enter a,b,c:");
            double a = scanner.nextDouble();
            double b = scanner.nextDouble();
            double c = scanner.nextDouble();
            double d=b*b-4*a*c;
            if(d>0){
                double r1=(-b+Math.pow(d,0.5))/(2*a);
                double r2=(-b-Math.pow(d,0.5))/(2*a);
                System.out.println("The equation has two roots "+r1+" and "+r2);
    
            }else if(d==0){
                double r=(-b)/(2*a);
                System.out.println("The equation has one root "+r);
            }else{
                System.out.println("The equation has no real roots");
            }
        }
    }

3.2

/**
     * 将三个数相加
     */
    public class T3_2 {
        public static void main(String[] args) {
            int number1 = (int) (System.currentTimeMillis() % 10);
            int number2 = (int) (System.currentTimeMillis() / 10 % 10);
            int number3 = (int) (System.currentTimeMillis() / 100 % 10);
            Scanner input = new Scanner(System.in);
            System.out.println("What is " + number1 + " + " + number2 + " + " + number3 + "? ");
            int answer = input.nextInt();
            System.out.println(
                    number1 + " + " + number2 + " + " + number3 + " = " + answer + " is " +
                            (number1 + number2 + number3 == answer));
        }
    }

3.3

import java.util.Scanner;
    
    /**
     * 求解2*2线性方程
     */
    public class T3_3 {
        public static void main(String[] args) {
            Scanner scanner=new Scanner(System.in);
            System.out.print("Enter a,b,c,d,e,f:");
            double a=scanner.nextDouble();
            double b=scanner.nextDouble();
            double c=scanner.nextDouble();
            double d=scanner.nextDouble();
            double e=scanner.nextDouble();
            double f=scanner.nextDouble();
            if(a*d-b*c==0){
                System.out.println("The equation has no solution");
            }else{
                double x=(e*d-b*f)/(a*d-b*c);
                double y=(a*f-e*c)/(a*d-b*c);
                System.out.println("x is "+x+" and y is "+y);
            }
        }
    }

3.4

/**
     * 随机月份
     */
    public class T3_4 {
        public static void main(String[] args) {
            int month = (int) (Math.random() * 12 + 1);
            System.out.println(month + "月");
            switch (month) {
                case 1:
                    System.out.println("January");
                    break;
                case 2:
                    System.out.println("February");
                    break;
                case 3:
                    System.out.println("March");
                    break;
                case 4:
                    System.out.println("April");
                    break;
                case 5:
                    System.out.println("May");
                    break;
                case 6:
                    System.out.println("June");
                    break;
                case 7:
                    System.out.println("July");
                    break;
                case 8:
                    System.out.println("August");
                    break;
                case 9:
                    System.out.println("September");
                    break;
                case 10:
                    System.out.println("October");
                    break;
                case 11:
                    System.out.println("November");
                    break;
                case 12:
                    System.out.println("December");
                    break;
            }
        }
    }

3.5

import java.util.Scanner;
    
    /**
     * 给出将来的日期
     */
    public class T3_5 {
        public static void main(String[] args) {
            Scanner scanner = new Scanner(System.in);
            System.out.print("Enter today's day:");
            int day = scanner.nextInt();
            System.out.print("Enter the number of days elapsed since today:");
            int days = scanner.nextInt();
            System.out.println("Today is " + getDays(day) + " and the future day is " + getDays((days + day) % 7));
        }
    
        public static String getDays(int day) {
            switch (day) {
                case 0:
                    return "Sunday";
                case 1:
                    return "Monday";
                case 2:
                    return "Tuesday";
                case 3:
                    return "Wednesday";
                case 4:
                    return "Thursday";
                case 5:
                    return "Friday";
                case 6:
                    return "Saturday";
                default:
                    return null;
            }
        }
    }

3.6

import java.util.Scanner;
    
    public class T3_6 {
        public static void main(String[] args) {
            Scanner scanner = new Scanner(System.in);
    
            System.out.print("Enter weight in pounds:");
            double weight = scanner.nextDouble();
            System.out.print("Enter feet:");
            double feet = scanner.nextDouble();//1 feet= 12inches
            System.out.print("Enter inches:");
            double inches = scanner.nextDouble();
    
            final double KILOGRAMS_PER_POUND = 0.45359237;
            final double METERS_PER_FEET = 0.3048;
    
            //Compute BMI
            double weightInKilograms = weight * KILOGRAMS_PER_POUND;
            double heightInMeters=((inches/12)+feet)*METERS_PER_FEET;
            double bmi=weightInKilograms/(heightInMeters*heightInMeters);
    
            //Display result
            System.out.println("BMI is "+bmi);
            if(bmi<18.5)
                System.out.println("Underweight");
            else if(bmi<25)
                System.out.println("Normal");
            else if(bmi<30)
                System.out.println("Overweight");
            else
                System.out.println("Obese");
        }
    }

3.9

import java.util.Scanner;
    
    /**
     * 检验ISBN-10
     */
    public class T3_9 {
        public static void main(String[] args) {
            Scanner scanner=new Scanner(System.in);
            int sum=0,num=1;
            System.out.print("Enter the first 9 digits of an ISBN as integer:");
            String isbn=scanner.next();
            for(int i=0;i<9;i++){
                int j=isbn.charAt(i)-'0';
                sum+=j*num++;
            }
            System.out.println("The ISBN-10 number is "+(((sum%11)==10)?(isbn+"X"):(isbn+(sum%11))));
        }
    }

3.15

import java.util.Scanner;
    
    /**
     * 彩票
     */
    public class T3_15 {
        public static void main(String[] args) {
            //Generate a lottery number
            int lottery = (int) (Math.random() * 1000);
            //Prompt the user to enter a guess
            Scanner input = new Scanner(System.in);
            System.out.print("Enter your lottery pick (three digits):");
            int guess = input.nextInt();
            //Get digits from lottery
            int lotteryDigit1 = lottery / 100;
            int lotteryDigit2 = lottery % 100 / 10;
            int lotteryDigit3 = lottery % 10;
            //Get digits from guess
            int guessDigit1 = guess / 100;
            int guessDigit2 = guess % 100 / 10;
            int guessDigit3 = guess % 10;
            System.out.println("The lottery number is " + lottery);
            //Check the guess
            if (guess == lottery) {
                System.out.println("Exact match: you win $10000");
            } else if (((guessDigit1 == lotteryDigit1) && (guessDigit2 == lotteryDigit3)
                    && (guessDigit3 == lotteryDigit2)) || ((guessDigit1 == lotteryDigit2) && (
                    guessDigit2 == lotteryDigit3) && (guessDigit3 == lotteryDigit1)) ||
                    ((guessDigit1 == lotteryDigit2) && (guessDigit2 == lotteryDigit1) && (guessDigit3 == lotteryDigit3)) ||
                    ((guessDigit1 == lotteryDigit3) && (guessDigit2 == lotteryDigit1) && (guessDigit3 == lotteryDigit2)) ||
                    ((guessDigit1 == lotteryDigit3) && (guessDigit2 == lotteryDigit2) && (guessDigit3 == lotteryDigit1))) {
                System.out.println("Match all digits: you win $3000");
            } else if ((guessDigit1 == lotteryDigit1) || (guessDigit1 == lotteryDigit2) || (guessDigit1 == lotteryDigit3) ||
                    (guessDigit2 == lotteryDigit2) || (guessDigit2 == lotteryDigit3) ||
                    (guessDigit3 == lotteryDigit3)) {
                System.out.println("Match one digits: you win $1000");
            } else {
                System.out.println("Sorry, no match");
            }
    
        }
    }