我想在 java 中使用递归打印一系列

Question

You have to print a pattern using recursion. Given a input N the pattern looks like this N, ai, ai + 1, ai + 2,....., N. Where if ai > 0 then ai + 1 = ai − 5 else ai + 1 = ai + 5. It will be a decreasing sequence from N till ai <= 0 and then an increasing sequence till N. (See sample test cases for better explanation)

Input format First line contains an integer T denoting number of test cases. For each of the next T lines, each line contains an integer N.

Output format For each test case on a new line, print the required pattern.

Constraints 1 <= T <= 6

0 <= N <= 2000

Example Input

2

16

10

Output

16 11 6 1 -4 1 6 11 16

10 5 0 5 10

Sample test case explanation For the first test case N=16, it will be a decreasing sequence till the printing number becomes <=0. 16 11 6 1 −4 After this point it will be a increasing sequence till the printing number becomes N 1 6 11 16 So the pattern is 16 11 6 1 −4 1 6 11 16.

My code is below but i got the output as 16,11,6,1,-4 only. Help me to correct this code

import java.util.Scanner;
public class Day3
{  
public static void series(int n,boolean b)
{
    int temp = n;
    boolean flag=b;
    System.out.println(temp+" ");
    if(flag==true)
        temp-=5;
    else if(flag==false)
        temp+=5;
    if(temp<=0)
        flag=false;
    if(temp<=n)
        series(temp,flag);
}
public static void main(String args[])
{
    Scanner sc = new Scanner(System.in);
    int t = sc.nextInt();
    while(t>0)
    {
        int n = sc.nextInt();
        series(n,true);
        t-=1;
    }
}
}

Answer 1

Because 'n' changes in every cases. You must create another variable and keep first 'n' in that, for control if temp smaller than 'n'.

For example

import java.util.Scanner;
public class Day3
{  

int firstN = 0; //added that line

public static void series(int n,boolean b)
{
    int temp = n;
    boolean flag=b;
    System.out.println(temp+" ");
    if(flag==true)
        temp-=5;
    else if(flag==false)
        temp+=5;
    if(temp<=0)
        flag=false;
    if(temp<=firstN) //changed that line
        series(temp,flag);
}
public static void main(String args[])
{
    Scanner sc = new Scanner(System.in);
    int t = sc.nextInt();
    while(t>0)
    {
        int n = sc.nextInt();
        firstN = n; //added that line
        series(n,true);
        t-=1;
    }
}
}

Also a little tip;

you can use (flag) for (flag==true)

and (!flag) for (flag==false)

Answer 2

Just FYI: Although this can be solved using recursion, it can be solved more efficiently without using recursion. It is as simple as this:

private static void printSeries(int N) {
      int T = N;
      while ( T >= 0 ) {
        System.out.print(T +  " ");
        T = T - 5;
      }
      while ( T <= N ) {
         System.out.print(T +  " ");
        T = T + 5;
      }
    }