RocketLogics

package com;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class RocketLogics {

	/** Please refer to https://gist.github.com/Wajahat-Jawaid/815da29116c18223ec365a3db745cea5
	 * for the test cases as multiple gists couldn't be linked */
	
	public static void main(String[] args) {
		// Arbitrary array.
		Object[] objArray = new Object[] {1, 4, new Object[] {43,434,34,2}, 3, new Object[]{1, 3, 4}};
		RocketLogics rocket = new RocketLogics();
		NestedArrayFlattener flattener = rocket.new NestedArrayFlattener();
		final Integer[] intArray = flattener.flatten(objArray);
	}
	
	class NestedArrayFlattener {

	    /**
	     * This method flattens an arbitrarily nested array of integers to return the flattened integer array.
	     *
	     * @param objArray an array of Integers or nested arrays of Integers
	     * @return flattened array of Integers or null if input is null
	     * @throws IllegalArgumentException
	     */
	    public Integer[] flatten(Object[] objArray) throws IllegalArgumentException {

	    	// If objArray is null, then no need to parse
	        if (objArray == null) return null;

	        // We can put the custom condition which handles Big O notation. But that totally depends upon the scenario
	        List<Integer> flattenedIntegers = new ArrayList<Integer>();

	        for (Object item : objArray) {
	            if (item instanceof Integer) {
	            	flattenedIntegers.add((Integer) item);
	            } else if (item instanceof Object[]) {
	            	// If nested array is found, perform recursion
	            	flattenedIntegers.addAll(Arrays.asList(flatten((Object[]) item)));
	            } else {
	                throw new IllegalArgumentException("Input array can contain only integer or nested integer array");
	            }
	        }
	        return flattenedIntegers.toArray(new Integer[flattenedIntegers.size()]);
	    }
	}
}