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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.*;
class TreeHeight {
static class FastScanner {
StringTokenizer tok = new StringTokenizer("");
BufferedReader in;
FastScanner(InputStream in) {
this.in = new BufferedReader(new InputStreamReader(System.in));
}
String next() throws IOException {
while (!tok.hasMoreElements())
tok = new StringTokenizer(in.readLine());
return tok.nextToken();
}
int nextInt() throws IOException {
return Integer.parseInt(next());
}
}
static class Node<T> {
private T key;
private Node<T> parent = null;
private List<Node<T>> children = new ArrayList<>();
Node(T key) {
this.key = key;
}
void addChild(Node<T> child) {
child.setParent(this);
this.children.add(child);
}
private void setParent(Node<T> parent) {
this.parent = parent;
}
public Node<T> getParent(Node<T> parent) {
return this.parent;
}
List<Node<T>> getChildren() {
return children;
}
public T getKey() {
return key;
}
void setKey(T key) {
this.key = key;
}
}
static int getHeight(int[] a) {
Node[] nodes = new Node[a.length];
int rootIndex = 0;
for (int i = 0; i < a.length; i++) {
nodes[i] = new Node<>(-5);
}
for (int i = 0; i < a.length; i++) {
int parentIndex = a[i];
if (parentIndex == -1) {
rootIndex = i;
nodes[i].setKey(i);
} else {
nodes[i].setKey(i);
nodes[parentIndex].addChild(nodes[i]);
}
}
return treeLevelCounter(nodes, rootIndex);
// return treeLevelCounterRecursive(nodes[rootIndex]);
}
private static int treeLevelCounterRecursive(Node<Integer> node) {
if (node.getChildren().size() == 0)
return 1;
int maxCount = Integer.MIN_VALUE;
int tempCount;
for (int i = 0; i < node.getChildren().size(); i++) {
tempCount = treeLevelCounterRecursive(node.getChildren().get(i));
if (tempCount > maxCount)
maxCount = tempCount;
}
return 1 + maxCount;
}
private static int treeLevelCounter(Node<Integer>[] nodes, int rootIndex) {
int levelCounter = 1;
Queue<Node<Integer>> q = new LinkedList<>();
int popCount = 0;
int childrenCount = nodes[rootIndex].getChildren().size();
int grandChildrenCount = 0;
for (int i = 0; i < childrenCount; i++) {
q.add(nodes[rootIndex].getChildren().get(i));
}
while (!q.isEmpty()) {
if (popCount < childrenCount) {
Node<Integer> n = q.remove();
int i = n.getChildren().size();
if (i != 0) {
for (int j = 0; j < i; j++) {
q.add(n.getChildren().get(j));
}
}
grandChildrenCount = grandChildrenCount + i;
popCount = popCount + 1;
} else {
popCount = 0;
childrenCount = grandChildrenCount;
grandChildrenCount = 0;
levelCounter = levelCounter + 1;
}
}
return levelCounter + 1;
}
static int getHeightNaive(int[] a) {
int n = a.length;
int maxHeight = 0;
for (int vertex = 0; vertex < n; vertex++) {
int height = 0;
for (int i = vertex; i != -1; i = a[i])
height++;
maxHeight = Math.max(maxHeight, height);
}
return maxHeight;
}
public static void main(String[] args) throws IOException {
FastScanner scanner = new FastScanner(System.in);
int n = scanner.nextInt();
int[] a = new int[n];
for (int i = 0; i < n; i++) {
a[i] = scanner.nextInt();
}
System.out.println(getHeight(a));
}
// public static void main(String[] args) {
// new Thread(null, new Runnable() {
// public void run() {
// try {
// runTheThing();
// } catch (IOException ignored) {
// }
// }
// }, "1", 1 << 26).start();
//
// }
//
// private static void runTheThing() throws IOException {
// FastScanner scanner = new FastScanner(System.in);
// int n = scanner.nextInt();
// int[] a = new int[n];
// for (int i = 0; i < n; i++) {
// a[i] = scanner.nextInt();
// }
// System.out.println(getHeight(a));
// }
}
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