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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 00000000 System.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"); } } }
