public int[] postOrder(int[] preorder, int[] inorder) {
        int[] post = new int[inorder.length];
        AtomicInteger postIndex = new AtomicInteger(post.length - 1);
        postOrder(preorder, inorder, post, 0, inorder.length -1, 0, postIndex);
        return post;
    }
Date 11/02/2015
@author Tushar Roy

Given a preorder/inorder traversal of binary tree create postorder traversal of binary tree
without creating the tree

Time complexity - O(n)

References
http://www.geeksforgeeks.org/print-postorder-from-given-inorder-and-preorder-traversals/
src/com/interview/tree/PrintPostOrderFromPreOrderInOrder.java