JAVA算法练习、排序练习

求1-100素数(质数)

for(int i = 2 ;i<=100;i++){
    boolean a = true;    //每次循环刷新
    for(int j = 2 ;j 
求1!+2!+...8!的和 (阶乘)
 
//求1!+2!+....+8!的和
int x,n = 1;
int sum = 0;
for(x=1; x<=8; x++)
{
    n *= x;   //逐步积累
    sum += n;
}
 
判断奇数偶数
 
Scanner input = new Scanner(System.in);
System.out.println("请输入一个数判断奇数偶数");
int number = input.nextInt();  //拿到输入的数然后继续判断
if(number%2 == 0){  //核心就是 %2 
    System.out.println(number+"是偶数");
}else{
    System.out.println(number+"是奇数");
}
 
判断是闰年还是平年
 
System.out.println("请输入年");
int years = input.nextInt();   
//能够被4整除又能够被100或者400整除的才是闰年
    if(years %4 == 0 && years %100 !=0 || years %400 == 0){  
        System.out.println(years+"是闰年");
    }else{
        System.out.println(years+"是平年");
    }
 
99乘法表
 
for(int i=1;i<=9;i++){
    for(int j=1;j<=i;j++){
        System.out.print(j+"x"+i+"="+(i*j));
    }
    System.out.println();
}
 
使用正则表达式验证用户和密码
 
(14条消息) JAVA:正则表达式基本使用；邮箱验证，手机号验证，split；_CXY_fengye的博客-CSDN博客
 
String st = "\d{5,9}";
String st1 = "[a-zA-Z]{5,20}";
System.out.println("请输入5-9为数字用户名");
String s = input.nextLine();
System.out.println("请输入密码");
String s1 = input.nextLine();
if(s1 != null){
    if(s.matches(st) && s1.matches(st1)){
        System.out.println("正确");
    }else{
        System.out.println("错误");
    }
}else{
    System.out.println("密码为空");
}
 
 
 
冒泡排序
 
int[] sorting = new int[]{2,9,5,6,7,8,0,1,4,3};
for(int i=0;isorting[j+1]){  //如果第j位大于j+1就交换
            int temp = sorting[j];
            sorting[j] = sorting[j+1];
            sorting[j+1] = temp;
        }
    }
}
 
选择排序
 
int[] sorting1 = new int[]{2,9,5,6,7,8,0,1,4,3};
for (int i=0;isorting1[j]){   //如果sorting1的第i位大于第j位就记录下来
            index = j;
        }
    }
    int temp = sorting1[index];
    sorting1[index] = sorting1[i];
    sorting1[i] = temp;
}
 
快速排序
 
int[] a = {1,35,23,2,4,13};
Arrays.sort(a);
for(int i:a){
    System.out.print(i+" ");
}