Pritning subarrays in a given array using recursion

Question

I am a beginner in Java programming and I am trying to print the subarrays in a given array using the concept of recursion.

I am getting my desired result but I am also getting some runtime errors.

My code:

import java.util.Scanner;

public class GFG {
    public static void printArrays(int[] arr, int start,int end,int n){
        for (int i = start; i <= end; i++){
            System.out.print(arr[i]+"");
        }
        System.out.print("\n");
    }
    public static void subArrays(int[] arr, int start, int end,int n) {
        if (end < n) {
            printArrays(arr, start, end, n);
            subArrays(arr, start, end + 1, n);
        }

        if (end >= n) {
            subArrays(arr, start + 1, start + 1, n);
        }

        if (start >= n) {
            return;
        }
    }

    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = scan.nextInt();
        }
        subArrays(arr, 0, 0, n);
    }
}

The error that I'm getting is this: 


Exception in thread "main" java.lang.StackOverflowError
    at GFG.subArrays(GFG.java:16)
    at GFG.subArrays(GFG.java:16)
    at GFG.subArrays(GFG.java:16)

The 16th line of code is "subArrays(arr,start+1,start+1,n);"

My output is this:

This means you're missing an end condition that will stop the recursion. Either stepping through the code, or (my preference) "playing computer" with paper and pencil, will help you to understand what's happening. — Dave Newton
– Dave Newton, Commented Mar 26, 2020 at 16:24
yes, I understand. But I cannot understand what I am missing. — Anubhuti Srivastava
– Anubhuti Srivastava, Commented Mar 26, 2020 at 16:26
Then step through it again; it's short enough it won't take long. — Dave Newton
– Dave Newton, Commented Mar 26, 2020 at 17:11
Recursion, once understood, will become much more intuitive. IMO paper/pencil or stepping through is the fastest way to understand it deeply--and once you do you'll find it in a lot of places. It's not suitable for everything, but when it is, it's like magic. — Dave Newton
– Dave Newton, Commented Mar 26, 2020 at 17:26
I get what you mean. I used to struggle a LOT with recursion, so I decided to start from the very basics and go ahead. I solved some questions with pen and paper for every stage. I then tried to solve questions with my intuition and I have started getting results! — Anubhuti Srivastava
– Anubhuti Srivastava, Commented Mar 26, 2020 at 18:02

Arvind Kumar Avinash · Accepted Answer · 2020-03-26 16:29:37Z

1

Your problem is because you are checking the condition for return (i.e. the value of start) at the end but before that, you are already calling printArrays(arr, start, end, n);, subArrays(arr, start + 1, start + 1, n); and subArrays(arr, start, end + 1, n); where the index is going beyond the limit. Put the following check at the beginning of subArrays:

if (start >= n) {
    return;
}

as follows:

public static void subArrays(int[] arr, int start, int end, int n) {
    if (start >= n) {
        return;
    }
    if (end < n) {
        printArrays(arr, start, end, n);
        subArrays(arr, start, end + 1, n);
    }    
    if (end >= n) {
        subArrays(arr, start + 1, start + 1, n);
    }
}

answered Mar 26, 2020 at 16:29

Arvind Kumar Avinash

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1 Comment

Anubhuti Srivastava Over a year ago

Thank you so much! This removed the error. Thanks a lot.

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