easyBasic Recursion

Reverse an Array using Recursion

Reverse the order of the values in an array using recursion.

GeeksforGeeks ↗

Work through the cases

3 examples

Input notation

One nonempty line of space-separated integers; at most 500 values.

Expected result

The reversed values, separated by spaces.

Case 1

Input

3 8 2 9

Expected output

9 2 8 3

Case 2

Input

Expected output

Case 3

Input

-2 0 -2

Expected output

-2 0 -2

These notes use simplified input/output notation. The linked platform defines the method signature and judge format.

FROM IDEA TO IMPLEMENTATION

Understand the approach.

Compare the documented approaches below. Brute force, better, and optimal versions appear where available; a direct exercise may need only one approach.

Swap the endpoints and recurse on the inner range until the pointers meet. Time: O(n); call-stack space: O(n).

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        ArrayList<Long> values = new ArrayList<>();
        while (in.hasNextLong()) values.add(in.nextLong());
        long[] a = values.stream().mapToLong(Long::longValue).toArray();
        long n = a[0];
        class R { void f(int l,int r){if(l>=r)return;long v=a[l];a[l]=a[r];a[r]=v;f(l+1,r-1);} } new R().f(0,a.length-1);for(long v:a)System.out.print(v+" ");
    }
}

Reference code. Platform solutions may use supplied node types, imports, or collection libraries; foundational examples are complete programs.