SCAU学习笔记 - 面向对象程序设计课后习题

复活啦！这学期给先给各位带来Java的题解后续的Bash可能也会有这篇自己也是边学边敲的算是共勉啦！

01-基础语法编程的知识点

摄氏温度值度转换成华氏温度值

java.util.Scanner是用来读入数据的，默认读入的是字符串
println输出的时候会自带一个回车，想输出两位小数的话就必须要转成字符串，占位规则和C语言没什么区别
变量的定义和计算赋值啥的都和C语言没啥区别就不多说了

java">import java.util.*;

public class one_one {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        double C = in.nextDouble();
        double F = C * 9 / 5 + 32;
        System.out.println(String.format("%.2f", F));
    }
}

圆柱体的体积

和上一题没有太大区别

java">import java.util.*;
import java.lang.*;

public class one_two {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        double r = in.nextDouble();
        double h= in.nextDouble();
        double V = Math.PI * r * r * h;
        System.out.println(String.format("%.2f", V));
    }
}

正整数的各位数字之和

nextLine可以直接读取一整行的内容作为字符串存进去
字符串的遍历，包括for循环的语法和取字符串长度都和C++没有差别

java">import java.util.*;
import java.lang.*;

public class one_three {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String s = in.nextLine();
        int res=0;
        for(int i=0;i<s.length();i++){
            res+=s.charAt(i)-'0';
        }
        System.out.println(res);
    }
}

三角形的面积

java">import java.util.*;
import java.lang.*;

public class one_four {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        double x1=in.nextDouble();
        double y1=in.nextDouble();
        double x2=in.nextDouble();
        double y2=in.nextDouble();
        double x3=in.nextDouble();
        double y3=in.nextDouble();
        double s1=Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
        double s2=Math.sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));
        double s3=Math.sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
        double s=(s1+s2+s3)/2;
        double area=Math.sqrt(s*(s-s1)*(s-s2)*(s-s3));
        System.out.println(String.format("area=%.2f", area));
    }
}

计算每个月第一天是星期几

开始写一些复杂的逻辑，我们先预处理每个月的天分，把闰年这样一个变量解决了，然后每个月累加天数计算即可

java">import java.util.*;
import java.lang.*;

public class One_five {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int year = in.nextInt();
        int first = in.nextInt();
        int[] days = {31,28,31,30,31,30,31,31,30,31,30,31};
        if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
            days[1] = 29;
        }
        int[] ans = new int[12];
        ans[0] = first;
        for (int i = 1; i < 12; i++) {
            ans[i] = (ans[i-1] + days[i-1]) % 7;
        }
        for (int i = 0; i < 12; i++) {
            System.out.print(ans[i]);
            if (i != 11) {
                System.out.print(" ");
            }
        }
    }
}

正整数10进制形式转换16进制形式

直接调函数，常见的进制转换一般都有内置函数的

java">import java.util.*;
import java.lang.*;

public class One_six {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        if(n < 0) {
            System.out.println("不正确的输入");
            return;
        }
        System.out.println(Integer.toHexString(n).toUpperCase());
    }
}

计算自然常数 e 的值

这题要注意一下浮点数和整数的计算规则啥的，如果学过C语言了那就都不成问题吧

java">import java.util.*;
import java.lang.*;

public class ont_seven {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        if(n < 0) {
            System.out.println("不正确的输入");
            return;
        }
        double e = 1;
        double temp = 1;
        for(int i = 1; i <= n; i++) {
            temp *= i;
            e += 1.0 / temp;
        }
        System.out.println(String.format("%.8f", e));
    }
}

判断回文整数

正常判断回文串即可，注意有负数的话要直接输出错误，所以要取字符串的第一个字符，和C语言有些不同，需要调一个函数

java">import java.util.*;
import java.lang.*;

public class One_eight {
    public static void main(String[] args) {
        String input = System.console().readLine();
        if(input.charAt(0) == '-') {
            System.out.println("不正确的输入");
            return;
        }
        int len = input.length();
        boolean flag = true;
        for (int i = 0; i < len / 2; i++) {
            if (input.charAt(i) != input.charAt(len - i - 1)) {
                flag = false;
                break;
            }
        }
        if (flag) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
    }
}

储物柜问题

注意数组开桶的语法

java">import java.util.Scanner;

public class One_nine {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int m = in.nextInt();
        boolean[] lockers = new boolean[m];
        for (int i = 0; i < m; i++) {
            lockers[i] = false;
        }
        for (int i = 1; i <= m; i++) {
            for (int j = i - 1; j < m; j += i) {
                lockers[j] = !lockers[j];
            }
        }
        for (int i = 0; i < m; i++) {
            if (lockers[i]) {
                System.out.print(i + 1 + " ");
            }
        }
    }
}

考试成绩分析

注意一下长度可变的数组是怎么开的

java">import java.util.*;
import java.lang.*;

public class One_ten {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[][] arr = new int[n][];
        for (int i = 0; i < n; i++) {
            int m = in.nextInt();
            arr[i] = new int[m];
            for (int j = 0; j < m; j++) {
                arr[i][j] = in.nextInt();
            }
        }

        for (int i = 0; i < n; i++) {
            int sum = 0;
            int max = arr[i][0];
            int min = arr[i][0];
            for (int j = 0; j < arr[i].length; j++) {
                sum += arr[i][j];
                if (arr[i][j] > max) {
                    max = arr[i][j];
                }
                if (arr[i][j] < min) {
                    min = arr[i][j];
                }
            }
            System.out.println(String.format("%.2f %.2f %.2f", (double) sum / arr[i].length, (double) max, (double) min));
        }
    }
}