Run

import java.util.*;

public class Main
{

// Binary tree class
  public static class BinaryTree
  {
// Node class
    public class Node
    {

      int data;
      Node left;
      Node right;

      public Node (int data)
      {
	this.data = data;
	this.left = null;
	this.right = null;
      }
    }

    private Node root;

    public BinaryTree (int[]pre, int[]post)
    {
      this.root =
	this.construct (pre, 0, pre.length - 1, post, 0, post.length - 1);

    }

    private Node construct (int[]pre, int presi, int preei, int[]post,
			    int postsi, int postei)
    {

// this case occurs when a node has only one child
      if (presi > preei)
	{
	  return null;
	}

      Node node = new Node (pre[presi]);
      node.left = null;
      node.right = null;

      if (presi == preei)
	{
	  return node;
	}

//Searching pre[presi + 1] in postorder array
      int pos = -1;
      for (int i = postsi; i <= postei; i++)
	{
	  if (post[i] == pre[presi + 1])
	    {
	      pos = i;
	      break;
	    }
	}

//Number of elements in left subtree
      int clc = pos - postsi + 1;

//Left subtree
      node.left =
	this.construct (pre, presi + 1, presi + clc, post, postsi, pos);

//Right subtree
      node.right =
	this.construct (pre, presi + clc + 1, preei, post, pos + 1,
			postei - 1);

      return node;
    }

    public int max ()
    {
      return this.max (this.root);
    }

//Function to find max in binary tree
    private int max (Node node)
    {

//Base case
      if (node == null)
	{
	  return Integer.MIN_VALUE;
	}

//Find max of left subtree
      int lmax = this.max (node.left);

//Find max of right subtree
      int rmax = this.max (node.right);

//Max of tree is max of left max, right max and the node data itsef.
      int rv = Math.max (node.data, Math.max (lmax, rmax));
      return rv;
    }
  }

  public static void main (String[]args) throws Exception
  {

// Construct binary tree

    int[] pre = { 50, 25, 12, 37, 30, 40, 75, 62, 60, 70, 87 };
    int[] post = { 12, 30, 40, 37, 25, 60, 70, 62, 87, 75, 50 };

    BinaryTree bt = new BinaryTree (pre, post);
    System.out.println ("Maximum of the tree is : " + bt.max ());

  }
}