判定一个数字是否是素数

public class Test {public static int is_sushu(int n) {if(n == 1) {return 0;}int i ;for (i = 2; i <= Math.sqrt(n); i++) {if(n % i == 0 ) {break;}}if (i > n) {return 1;}return 0;}public static void main(String[] args) {Scanner scanner = new Scanner(System.in);int n = scanner.nextInt();int ret = is_sushu(n);if(ret == 1 ) {System.out.println(n + "是素数");} else {System.out.println(n + "不是素数");}}
}

  输出 1000 - 2000 之间所有的闰年

public class Test {public static void main(String[] args) {int year ;for ( year = 1000; year <= 2000 ; year++) {if(year % 4 ==0 && year % 100 !=0 || year % 400 == 0 ){System.out.println(year + "是闰年");}}}
}

 输出乘法口诀表

public class Test {public static void main(String[] args) {for (int i = 1; i <= 9; i++) {for (int j = 1; j <= i ; j++) {System.out.print(i + "*" + j + "=" + i*j + " ");}System.out.println();}}
}

 求两个正整数的最大公约数

public class Test {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);int a = scanner.nextInt();int b = scanner.nextInt();if(b > a) {int tmp = b;b = a;a = b;}int c =a % b;while(c != 0) {a = b;b = c;c = a % b;}System.out.println(b);}
}

 求出0～999之间的所有“水仙花数”并输出。(“水仙花数”是指一个三位数，其各位数字的立方和确好等于该数
本身，如： 153＝1^3＋5^3＋3^3 ，则153是一个“水仙花数”。)

public class Test {public static void main(String[] args) {int i;for (i = 100; i < 1000 ; i++) {int k = i;int sum = 0;while(k != 0) {sum+=Math.pow(k%10,3);k /= 10;}if (sum == i) {System.out.println(i);}}}
}

 写一个函数返回参数二进制中 1 的个数
比如： 15 0000 1111 4 个 1

import java.util.Scanner;
public class Test {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);int n = scanner.nextInt();int count = 0;/*for (int i = 0; i < 32; i++) {if ((n >> i & 1) == 1) {count++;}}*/while (n != 0) {count++;n = n & (n-1);}System.out.println(count);}
}

 获取一个数二进制序列中所有的偶数位和奇数位，分别输出二进制序列。

import java.util.Scanner;
public class Test {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);int n = scanner.nextInt();int i;// 00000000 00000000 00000000 00001010// 00000000 00000000 00000000 00000001// 00000000 00000011// 00000000 00000000System.out.print("偶数位：");for ( i = 31; i > 0; i-=2) {if((n >> i & 1) == 1) {System.out.print(1 + " ");} else {System.out.print(0 + " ");}}System.out.println("");System.out.print("奇数位：");for ( i = 30; i >= 0; i-=2) {if((n >> i & 1) == 1) {System.out.print(1 + " ");} else {System.out.print(0 + " ");}}}
}

 

 猜数字游戏

import java.util.Random;
import java.util.Scanner;public class Test {public static void main(String[] args) {//获取随机数Random random = new Random();Scanner scanner = new Scanner(System.in);int n = random.nextInt(100);// [0,100)int count =  3;while (count != 0) {System.out.println("输入你的数字");int ret = scanner.nextInt();if(ret > n) {System.out.println("猜大了");} else if(ret < n) {System.out.println("猜小了");} else {System.out.println("恭喜你猜对了");break;}count--;if(count == 0) {System.out.println("你没有机会了");break;}System.out.println("你还有" + count + "机会");}}
}