Minimum value node having maximum depth in an N-ary Tree

import java.util.Vector;
import java.util.ArrayList;
// Java program for
// Minimum value node having maximum depth in an N-ary Tree
class TreeNode
{
	public int key;
	public Vector < TreeNode > child;
	public TreeNode(int key)
	{
		this.key = key;
		this.child = new Vector < TreeNode > ();
	}
	public void addChild(int key)
	{
		TreeNode t = new TreeNode(key);
		this.child.add(t);
	}
}
public class NAryTree
{
	public TreeNode root;
	public int result;
	public NAryTree()
	{
		// Set initial tree root to null
		this.root = null;
		this.result = 0;
	}
	public int max(int a, int b)
	{
		if (a > b)
		{
			return a;
		}
		else
		{
			return b;
		}
	}
	// Returns the height of n ary tree
	public int findHeight(TreeNode node)
	{
		if (node == null)
		{
			return 0;
		}
		int i = 0;
		int depth = 0;
		// iterating the child of given node
		while (i < node.child.size())
		{
			// Recursively visit child node
			depth = max(findHeight(node.child.get(i)), depth);
			i++;
		}
		return depth + 1;
	}
	// Find minimum node in maximum depth using recursion
	public void minNode(TreeNode node, int depth)
	{
		if (depth == 1)
		{
			if (this.result > node.key)
			{
				// Get the value of resultant node
				this.result = node.key;
			}
		}
		else
		{
			int i = 0;
			// iterating the child of given node
			while (i < node.child.size())
			{
				// Recursively visit child node
				minNode(node.child.get(i), depth - 1);
				i++;
			}
		}
	}
	// Handles the request to find minimum node in maximum depth
	public void minValueMaxDepth()
	{
		if (this.root == null)
		{
			return;
		}
		// Find the height of tree
		int depth = findHeight(this.root);
		if (depth == 1)
		{
			// When single node exists in tree
			this.result = this.root.key;
		}
		else
		{
			this.result = Integer.MAX_VALUE;
			// Find minimum node
			minNode(this.root, depth);
		}
		// Display the minimum value in maximum depth nodes
		System.out.print(" Minimum node at maximum depth : " + this.result);
	}
	public static void main(String[] args)
	{
		NAryTree tree = new NAryTree();
		/*
		           10
		          /   \
		         /     \
		        /       \   
		       8         5
		      /|\      /|\ \ 
		     / | \    / | \ \
		    -2 1  6  7 18 3  4
		      / \           /| \
		     9  11         2 1  3
		       /  \        |
		      17   12      20
		    
		    -----------------------
		    Constructing N-Arr tree
		*/
		// First element of tree
		tree.root = new TreeNode(10);
		tree.root.addChild(8);
		tree.root.addChild(5);
		// Add child node [-2,1,5] in node (8)
		tree.root.child.get(0).addChild(-2);
		tree.root.child.get(0).addChild(1);
		tree.root.child.get(0).addChild(6);
		// Add child node [9,11] in node (1)
		tree.root.child.get(0).child.get(1).addChild(9);
		tree.root.child.get(0).child.get(1).addChild(11);
		// Add child node [17  12] in node (11)
		tree.root.child.get(0).child.get(1).child.get(1).addChild(17);
		tree.root.child.get(0).child.get(1).child.get(1).addChild(12);
		// Add child node [7 18 3  4] in node (5)
		tree.root.child.get(1).addChild(7);
		tree.root.child.get(1).addChild(18);
		tree.root.child.get(1).addChild(3);
		tree.root.child.get(1).addChild(4);
		// Add child node [2,1,3] in node (4)
		tree.root.child.get(1).child.get(3).addChild(2);
		tree.root.child.get(1).child.get(3).addChild(1);
		tree.root.child.get(1).child.get(3).addChild(3);
		// Add child node [20] in node (2)
		tree.root.child.get(1).child.get(3).child.get(0).addChild(20);
		tree.minValueMaxDepth();
	}
}

input

 Minimum node at maximum depth : 12