一、基础练习

1.A+B的问题

package Chapter01;

import java.util.Scanner;

//A+B的问题
public class Demo01 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt();
        int b = scanner.nextInt();
        System.out.println(a+b);
    }
}

2.Fibonacci数列

package Chapter01;

import java.util.Scanner;

//Fibonacci数列
public class Demo02 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        if (n<3){
            System.out.println(1);
        }else {
            int[] a = new int[n+1];
            a[1] = 1%10007;
            a[2] = 1%10007;
            for (int i = 3; i <=n ; i++) {
                a[i] = (a[i-1]+a[i-2])%10007;
            }
            System.out.println(a[n]);
        }
    }
}

3.序列求和

package Chapter01;

import java.util.Scanner;

//序列求和
public class Demo03 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long n = scanner.nextLong();
        long sum = 0;
        for (int i = 1; i <=n ; i++) {
            sum = sum+i;
        }
        System.out.println(sum);
    }
}

4.圆的面积

package Chapter01;

import java.util.Scanner;

//圆的面积
public class Demo04 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        final double PI = 3.14159265358979323;
        double r = scanner.nextInt();
        double s = r*r*PI;
        System.out.println(String.format("%.7f",s));//保留七位小数。
    }
}

5.十六进制转八进制

package Chapter01;

import java.util.Scanner;

//十六进制转八进制
public class Demo05 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        String[] a = new String[n];
        for (int i = 0; i < n; i++) {
            a[i] = scanner.next();
        }
        scanner.close();
        for (int j = 0; j < n; j++) {
            String str2 = f(a[j]);
            int len2 = str2.length();
            if (len2%3==1){str2="00"+str2;}
            if (len2%3==2){str2="0"+str2;}
            g(str2);
        }
    }


    public static String f(String s){
        int len = s.length();
        StringBuilder str = new StringBuilder();
        for (int i = 0; i < len; i++) {
            switch (s.charAt(i)){
                case '0':str.append("0000");break;
                case '1':str.append("0001");break;
                case '2':str.append("0010");break;
                case '3':str.append("0011");break;
                case '4':str.append("0100");break;
                case '5':str.append("0101");break;
                case '6':str.append("0110");break;
                case '7':str.append("0111");break;
                case '8':str.append("1000");break;
                case '9':str.append("1001");break;
                case 'A':str.append("1010");break;
                case 'B':str.append("1011");break;
                case 'C':str.append("1100");break;
                case 'D':str.append("1101");break;
                case 'E':str.append("1110");break;
                case 'F':str.append("1111");break;
                default:break;
            }
        }
        return str.toString();
    }


    public static void g(String str) {
        int len = str.length();
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < len; i=i+3) {
            int temp = ((str.charAt(i)-'0')*4+(str.charAt(i+1)-'0')*2+(str.charAt(i+2)-'0'));//二进制变八进制
            s.append(temp);
        }
        System.out.println(s.toString().replaceFirst("^0*",""));
        //正则表达式：^:匹配输入字符串的开始位置;   *:匹配前面的子表达式零次或多次。
    }
}

6.数列排序

package Chapter01;

import java.util.Scanner;

//数列排序
public class Demo06 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        int temp;
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
        }
        for (int j = 0; j < n; j++) {
            for (int i = 0; i < n-j-1; i++) {
                if (arr[i]>arr[i+1]){
                    temp=arr[i];
                    arr[i]=arr[i+1];
                    arr[i+1]=temp;
                }
            }
        }
        for (int i = 0; i < n; i++) {
            System.out.print(arr[i]+" ");
        }
        sc.close();
    }
}

7.十六进制转十进制

package Chapter01;

import java.util.Scanner;

//十六进制转十进制
public class Demo07 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String string = scanner.next();
        //装箱,可转换为十进制long型整数。
        System.out.println(Long.valueOf(string,16));
        //拆箱。
        System.out.println(Long.parseLong(string,16));
    }
}

8.十进制转十六进制

package Chapter01;

import java.util.Scanner;

//十进制转十六进制
public class Demo08 {
    //方法一
    /*public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        System.out.println(String.format("%X",n));//转换为大写的十六进制整数类型。
    }*/

    //方法二
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        //Integer.toHexString(n)表示把十进制表示为十六进制。
        //toUpperCase())表示把十六进制中的小写字母转换为大写字母。
        System.out.println(Integer.toHexString(n).toUpperCase());
    }
}

9.杨辉三角型

package Chapter01;

import java.util.Scanner;

//杨辉三角型
//number = number*(i-j)/(j+1);
//题目要求 1 <= n <= 34.要用long类型。
public class Demo09 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        for (int i = 0; i < n; i++) {
            long number = 1;
            for (int j = 0; j <= i; j++) {
                System.out.print(number+" ");
                number = number*(i-j)/(j+1);
            }
            System.out.println();
        }
    }
}

10.回文数

package Chapter01;

//回文数
public class Demo10 {
    public static void main(String[] args) {
        for (int i = 1; i < 10; i++) {
            for (int j = 0; j < 10; j++) {
                System.out.println(i+""+j+""+j+""+i);
            }
        }
    }
}

11.特殊回文数

package Chapter01;

import java.util.Scanner;

//特殊回文数
public class Demo11 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        for (int i = 1; i <10 ; i++) {
            for (int j = 0; j <10 ; j++) {
                for (int k = 0; k < 10; k++) {
                    if (i+i+j+j+k==n){
                        System.out.println(""+i+j+k+j+i);
                    }
                }
            }
        }
        for (int i = 1; i <10 ; i++) {
            for (int j = 0; j <10 ; j++) {
                for (int k = 0; k < 10; k++) {
                    if (i+i+j+j+k+k==n){
                        System.out.println(""+i+j+k+k+j+i);
                    }
                }
            }
        }
    }
}

12.特殊的数字

package Chapter01;

//特殊的数字
public class Demo12 {
    public static void main(String[] args) {
        for (int i = 1; i < 10; i++) {
            for (int j = 0; j < 10; j++) {
                for (int k = 0; k < 10; k++) {
                    if ((i*i*i+j*j*j+k*k*k)==(i*100+j*10+k)){
                        System.out.println(""+i+j+k);
                    }
                }
            }
        }
    }
}

13.查找整数

package Chapter01;

import java.util.Scanner;

//查找整数
public class Demo13 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = scanner.nextInt();
        }
        int a = scanner.nextInt();
        scanner.close();

        for (int j = 0; j < n; j++) {
            if (arr[j]==a){
                System.out.println(j+1);
                break;//也可以设置一个标志位。
            }else if (j==n-1){//假如到最后以为也没找到整数。
                System.out.println(-1);
            }
        }
    }
}

14.数列特征

package Chapter01;

import java.util.Scanner;

//数列特征
public class Demo14 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i]=scanner.nextInt();
        }
        scanner.close();

        int sum=0,max=arr[0],min=arr[0];
        for (int i = 0; i < n; i++) {
            if (min>arr[i]){
                min=arr[i];
            }
            if (max<arr[i]){
                max=arr[i];
            }
            sum = sum+arr[i];
        }
        System.out.println(max);
        System.out.println(min);
        System.out.println(sum);
    }
}

15.字母图形

package Chapter01;

import java.util.Scanner;

//字母图形
public class Demo15 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int m = scanner.nextInt();
        scanner.close();

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                char x = (char)('A'+Math.abs(i-j));//Math.abs(i-j) 技巧
                System.out.print(x);
            }
            System.out.println();
        }
    }
}

16.01字串

package Chapter01;

//01字串
public class Demo16 {
    public static void main(String[] args) {
        for (int i = 0; i < 2; i++) {
            for (int j = 0; j < 2; j++) {
                for (int k = 0; k < 2; k++) {
                    for (int l = 0; l < 2; l++) {
                        for (int m = 0; m < 2; m++) {
                            System.out.println(""+i+j+k+l+m);
                        }
                    }
                }
            }
        }
    }
}

17.闰年判断

package Chapter01;

import java.util.Scanner;

//闰年判断
public class Demo17 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int y = scanner.nextInt();
        if ((y%4==0&&y%100!=0) || y%400==0){
            System.out.println("yes");
        }else {
            System.out.println("no");
        }
    }
}