Party.java

/**
 * @author bertolo1988
 * http://codeforces.com/problemset/problem/115/A
 * 115A-Party
 */
import java.util.*;

public class Party {

	public static void main(String[] args) {
		Scanner keyboard = new Scanner(System.in);
		LinkedHashMap<String, String> bossesMap = new LinkedHashMap<String, String>();
		int n = keyboard.nextInt();
		for (int i = 1; i <= n; i++) {
			String parentLabel = keyboard.next();
			if (!parentLabel.equals("-1") && parentLabel.length() > 0) {
				bossesMap.put(Integer.toString(i), parentLabel);
			} else {
				bossesMap.put(Integer.toString(i), null);
			}
		}
		System.out.println(retrieveMinimumPartyGroups(bossesMap));
		keyboard.close();
	}

	private static int retrieveMinimumPartyGroups(LinkedHashMap<String, String> bossesMap) {
		TreeSet<String> depths = new TreeSet<String>();
		bossesMap.keySet().forEach(key -> depths.add(calcDepth(key, bossesMap)));
		return depths.size();
	}

	private static String calcDepth(String key, LinkedHashMap<String, String> bossesMap) {
		int depth = 1;
		for (String cursor = bossesMap.get(key); cursor != null; cursor = bossesMap.get(cursor)) {
			depth++;
		}
		return Integer.toString(depth);
	}
}