How to reverse a sequence of numbers with recursion in java

Question

I'm quite stuck on this piece of code, the assignment is simple: "given a number n or value, print on the console the sequence from n to 1 and from 1 to n (repeating the number 1 so it should be like this '5432112345').

The recursion per se is not a problem, the real problem is the second part due to the fact that i cannot use any other variable only n. I cannot store the starting value nowhere, since each time i call the method it would be actualized.

Here is the code so far:

public int mirrorRecursive(Integer value){
       if (value < 1){        //in case the given value is less than 1 it won't print anything
            return value;
        }
        if(value == 1){        //in case the value is 1, it will be printed and stop the calling
            System.out.print(value);
        }else{                 //in case the value is not 1 or less, it will print and call again the method
            System.out.print(value);
            mirrorRecursive(--value);
        }

        return value;
}

You shouldn't really use Stackoverflow to solve classroom assignments. — user1485864
– user1485864, Commented Jan 7, 2020 at 16:11
Actually i think is a good tool to use, either you are a student or a professional programmer. It's not always easy to understand a concept, or maybe you just miss a simple step. Everyone has the right to ask and sound stupid, if the purpose is to learn. — Simone Nardone
– Simone Nardone, Commented Jan 11, 2020 at 16:24

Eran · Accepted Answer · 2020-01-07 13:45:40Z

5

I'm not sure what's the use of the value returned by the method, but in order to print the desired output, all you need is:

public static int mirrorRecursive(Integer value){
  System.out.print(value);
  if (value > 1) {
    mirrorRecursive(value - 1);
  }
  System.out.print(value);

  return value;
}

i.e. print the current number before and after the recursive call, and make a recursive call as long as value > 1.

answered Jan 7, 2020 at 13:45

Eran

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1 Comment

user1485864 Over a year ago

This is the answer, but I don't think that in stackoverflow we should solve homework assignments ;-) And as an improvement the method can be void.

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