CodeWars Challenge: John and Ann sign up for CodeWars (Uncomplete)

Johnann.java

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

/*
	I was unable to complete this as I had overlooked how to manage 2 lists at once, providing
	checks on when to fill what array. I had kept a linear fashion of thinking that each had to be
	incremented every iteration, which was invalid.

	On the other hand, using this solution, we add values based on whether the other has it, rather
	than ensuring both lists are updated simultaneously
 */

public class Johnann {
	enum Person {
		JOHN, ANN;
	}

	private static List<Long> generateLists (Person person, long n) {
		List<Long> john = new ArrayList<Long>(Collections.singletonList(0L));
		List<Long> ann = new ArrayList<Long>(Collections.singletonList(1L));

		for (int dayAnn = 1, dayJohn = 1; dayAnn < n || dayJohn < n;) {
			if (john.size() > ann.get(dayAnn - 1)) {
				ann.add(dayAnn - john.get(Math.toIntExact(ann.get(dayAnn - 1))));
				dayAnn++;
			}

			if (ann.size() > john.get(dayJohn - 1)) {
				john.add(dayJohn - ann.get(Math.toIntExact(john.get(dayJohn - 1))));
				dayJohn++;
			}
		}

		return (person == Person.JOHN ? john : ann);
	}

	public static List<Long> john(long n) {
		return generateLists(Person.JOHN, n - 1);
	}
	public static List<Long> ann(long n) {
		return generateLists(Person.ANN, n);
	}
	public static long sumJohn(long n) {
		return generateLists(Person.JOHN, n - 1).stream().mapToLong(l -> l).sum();
	}
	public static long sumAnn(long n) {
		return generateLists(Person.ANN, n).stream().mapToLong(l -> l).sum();
	}
}