Practical small cases of java development basics

1. Recursive algorithm Find a certain number in the Fibonacci sequence

import java.util.Scanner;
public class diguisuanfa {
 public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int a=sc.nextInt();
    System.out.println(getNum(a));
}
 public static int getNum(int n ) {
     if(n<1) {
     System.out.println("输入不合法");
        return 0;
     }
     if(n==1|n==2) {
         return 1;
     }else {
        return getNum(n-2)+getNum(n-1);
     }    
 }
}

2. Sum the Fibonacci sequence

package CSDN;
import java.util.Scanner;
public class diguisuanfa {
    
     static int sum=0;
 public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int a=sc.nextInt();
    for(int i=1;i<=a;i++) {
        sum+=getNum(i);
    }
    System.out.println(sum);
}
 
 public static int getNum(int n ) {
     if(n<1) {
     System.out.println("输入不合法");
        return 0;
     }
     if(n==1|n==2) {
         return 1;
     }else {
        return getNum(n-2)+getNum(n-1);
     }
 }
}

3. Find the sum of 1~a certain number The sum of all integers between

//求1~某个数之间所有整数的和
public class qiuhe {
static int sum=0;
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n =sc.nextInt();
System.out.println(getNum(n));
}
public static int getNum(int n) {
if(n==1) {
return 1;
}else if(n>=1){
return n+getNum(n-1);
}else {
return getNum(n-1);
}
}
}

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