CareerCup_4.5 - Check if binary tree is BST

BSTChecker.java

package Chapter4;

import java.util.Stack;

public class BSTChecker {
    public static <T extends Comparable<T>> boolean isBST(BinaryTree<T> tree) {
	Stack<TreeNode<T>> stack = new Stack<>();
	TreeNode<T> cur = tree.root();
	T prevKey = null;

	while (cur != null || !stack.isEmpty()) {
	    while (cur != null) {
		stack.push(cur);
		cur = cur.left;
	    }

	    if (!stack.isEmpty()) {
		cur = stack.pop();
		if (prevKey != null && cur.key.compareTo(prevKey) < 0) {
		    return false;
		}
		prevKey = cur.key;
		cur = cur.right;
	    }
	}

	return true;
    }
    
    public static void main(String[] args) {
	/*	_______7______
	       /              \
	    __10__          ___2
	   /      \        /
	   4       3      _8
	            \    /
	             1  11 		*/
	Integer[] pre = { 7, 10, 4, 3, 1, 2, 8, 11 };
	Integer[] in = { 4, 10, 3, 1, 7, 11, 8, 2 };
	BinaryTree<Integer> bt1 = BinaryTreeBuilder.buildTree(pre, in);
	System.out.println("tree A is BST: " + isBST(bt1));
	
	/*	_______7______
	       /              \
	    __2__          __11
	   /     \        /
	   1      3      10
	           \    /
	            4  8 		*/
	Integer[] pre2 = { 7, 2, 1, 3, 4, 11, 10, 8 };
	Integer[] in2 = { 1, 2, 3, 4, 7, 8, 10, 11 };
	BinaryTree<Integer> bt2 = BinaryTreeBuilder.buildTree(pre2, in2);
	System.out.println("tree B is BST: " + isBST(bt2));
    }
}