static class Node {

int data;

Node left, right;

}

// temporary node to keep track of Node returned

// from previous recursive call during backtrack

static Node temp = null;

static int k;

// recursive function to calculate Kth ancestor

static Node kthAncestorDFS(Node root, int node ) {

// Base case

if (root == null)

return null;

if (root.data == node|| (temp = kthAncestorDFS(root.left,node)) != null || (temp = kthAncestorDFS(root.right,node)) != null) {

if (k > 0)

k--;

else if (k == 0) {

// print the kth ancestor

System.out.print("Kth ancestor is: "+root.data);

// return null to stop further backtracking

return null;

}

// return current node to previous call

return root;

}

return null;

}

// Utility function to create a new tree node

static Node newNode(int data) {

Node temp = new Node();

temp.data = data;

temp.left = temp.right = null;

return temp;

}

// Driver code

public static void main(String[] args) {

// Let us create binary tree shown in above diagram

Node root = newNode(1);

root.left = newNode(2);

root.right = newNode(3);

root.left.left = newNode(4);

root.left.right = newNode(5);

k = 2;

int node = 5;

// print kth ancestor of given node

Node parent = kthAncestorDFS(root,node);

// check if parent is not null,

// it means there is no Kth ancestor of the node

if (parent != null)

System.out.println("-1");

}