记JAVA基础:倒立正三角形、数组大小排序、水仙花数、青蛙跳

#eclipse自动补全

#添加（表示所有字母都可以自动补全）

.abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ

#倒立正三角形
public class test {
	public static void main(String[] args) {
		int i,j;
		for (i = 0; i <=4; i++) {
			for ( j = 0; j <= 4 - i; j++) {
				System.out.print("*");
			}
			System.out.println();
		}
	}

}

#数组大小排序
import java.util.Arrays;

public class arrtest {
	public static void main(String[] args) {
		System.out.println("请输入数组个数：");
		int c = getint();
		
		int[] arr = new int[c];
		for (int i = 0; i < c; i++) {
			System.out.println("请输入第"+(i+1)+"整数");
			arr[i]=getint();
		}
		System.out.println("排序前："+Arrays.toString(arr));
		paixu(arr);
		
	}

	private static void paixu(int[] arr) {
		int b;
		for (int i = 0; i < arr.length; i++) {
			for (int j = i+1; j < arr.length; j++) {
				if (arr[i] < arr[j]) {
					b = arr[i];
					arr[i] = arr[j];
					arr[j] = b;
				}
			}
		}
		System.out.println("排序后："+Arrays.toString(arr));
		
	}
	private static int getint() {
		Scanner sc = new Scanner(System.in);
		return sc.nextInt();
	}

}

#水仙花数：是指一个三位数，其各位数字立方和等于该数本身
package test;

import java.util.Scanner;

public class shuixianhua {
	public static void main(String[] args) {
		for (int i = 100; i < 1000; i++) {
			int q = i % 10;
			int w = (i / 10) % 10;
			int e = i /100;
			if (i == (q*q*q)+(w*w*w)+(e*e*e)) {
				System.out.println(i);
			}
		}
	}
}

求s=a+aa+aaa+aaaa+aa...a

package test;

import java.util.Scanner;

public class testtest {
	public static void main(String[] args) {
		System.out.println("请输入相加次数:");
		int a =getint();
		System.out.println("请输入数值:");
		int b =getint1();
		int first =b;
		int s = 0;
		for (int i = 0; i < a; i++) {
            s += b;
            b = b * 10 + first;
        }
		
		 System.out.println("相加后的值为："+s);
		
	}
	private static int getint1() {
		Scanner sc = new Scanner(System.in);
		return sc.nextInt();
	}

	private static int getint() {
		Scanner sc = new Scanner(System.in);
		return sc.nextInt();
	}

	
}

#青蛙跳一只青蛙一次可以跳1级或2级台阶，N级的台阶总共有多少种跳法
分析：
/**
1层：1种
2层： 2种
3层:   3种
4层:    5种
5层:      8种
6层:       13种
7层          21种
总结规律
2层=1层+1层
3层=1层+2层
4层=2层+3层
5层=3层+4层
6层=4层+5层
7层=5层+6层
**/
第一种写法
 public static void main(String[] args){
	        System.out.println("请输入台阶数：");
	        try (Scanner input = new Scanner(System.in)) {
	            int n=input.nextInt();
                            //frogjump方法
	            long result = frogjump(n);
				// long result = (int)Math.pow(n-3, 2)+1;
	            System.out.println("共有"+result+"种方法");
	        }
	    }
//frogjump计算方法
		static int frogjump(int n ){
        if(n==1){
            return 1;
        }else if(n==2){
            return 2;
        }else{
            int a = 1;
            int b = 2;
            int tmp = 0;
            for(int i=3;i<=n;i++){
                tmp = a+b;
                a = b;
                b = tmp;
            }
            return tmp;
        }
		}

第二种写法
public static void main(String[] args){
	        System.out.println("请输入台阶数：");
	        try (Scanner input = new Scanner(System.in)) {
	            int n=input.nextInt();
                            //调用jump方法
	            long result = jump(n);
	            System.out.println("共有"+result+"种方法");
	        }
	    }
//jump计算方法
	 public static int jump(int n){
	        if(n==0){
	            return 0;
	        }
	        else{
	        int[] frog=new int[3];
	        frog[0]=1;
	        frog[1]=2;
	        for(int i=2;i<n;i++){
	            frog[i%3]=frog[(i-1)%3]+frog[(i-2)%3];
	        }
			//返回跳的次数
	        return frog[(n-1)%3];
	    }
}
第N总解法---，掌握数学规律后，想咋写就咋写

#这天是一年的第几天？
public static void main(String[] args){
        System.out.println("----这一天是这一年的第几天-----");
       //设置日期格式
	    SimpleDateFormat simpleDate = new SimpleDateFormat("yyyy/MM");
	    Scanner sc =new Scanner(System.in);
	    System.out.println("请输入年份");
	    String dyear=sc.nextLine(); 
	    System.out.println("请输入月份");
	    String dmouth=sc.nextLine();
	    System.out.println("请输入日");
	    int dayint =sc.nextInt();
	    Calendar rightNow = Calendar.getInstance();
	    int daysum=0;
	    try{
		    int a =Integer.parseInt(dmouth);
		    for (int i = 1; i < a; i++) {
		    	rightNow.setTime(simpleDate.parse(dyear+"/"+i));
		    	int days=0;
		    	days =rightNow.getActualMaximum(Calendar.DAY_OF_MONTH);
		    	System.out.print(i+"月:"+days+"天"+" ");
		    	daysum +=days;
			}
	    }catch(ParseException e){e.printStackTrace();}
	    System.out.println("\n"+"年第："+(daysum+dayint)+"天");
	     //getActualMaximum获取天数最大值
	    int days = rightNow.getActualMaximum(Calendar.DAY_OF_MONTH);//根据年月 获取月份天数
	    System.out.println(days);
	}