Merge pull request blakeembrey#121 from roitt/binary-search-tree-check

Binary search tree check

Author: blakeembrey

solutions/java/BinarySearchTreeCheck.java

@@ -0,0 +1,105 @@
+/* Uses Inorder traversal. Only works on unique element BT */
+public class BinarySearchTreeCheck {
+	Node root;
+
+	public BinarySearchTreeCheck() {
+		root = null;
+	}
+
+	public class Node {
+		int value;
+		Node left;
+		Node right;
+
+		public Node(int value) {
+			this.value = value;
+			this.left = null;
+			this.right = null;
+		}
+
+		public void setLeft(Node left) {
+			this.left = left;
+		}
+
+		public Node getLeft() {
+			return left;
+		}
+
+		public void setRight(Node right) {
+			this.right = right;
+		}
+
+		public Node getRight() {
+			return right;
+		}
+
+		public int getValue() {
+			return value;
+		}
+	}
+
+	public void createBinaryTree(int option) {
+		root = new Node(10);
+		Node one = new Node(8);
+		Node two = new Node(5);
+		Node three = new Node(9);
+		Node four = new Node(15);
+		switch (option) {
+		case 1: /* Is BST (Only unique elements) */
+			root.setLeft(one);
+			root.setRight(four);
+			one.setLeft(two);
+			one.setRight(three);
+			break;
+		case 2: /* Not BST (Only unique elements) */
+			root.setRight(two);
+			root.setLeft(one);
+			one.setLeft(four);
+			one.setRight(three);
+			break;
+		default:
+			break;
+		}
+	}
+
+	public boolean isBSTBetter() {
+		if (root == null)
+			return true;
+		return isBSTBetter(root);
+	}
+
+	private Integer prev = null;
+
+	public boolean isBSTBetter(Node cur) {
+		if (cur == null)
+			return true;
+
+		// Check for the left subtree
+		if (!isBSTBetter(cur.getLeft())) {
+			return false;
+		}
+
+		// Check the cur value and update prev
+		if (prev != null && cur.getValue() <= prev)
+			return false;
+		prev = cur.getValue();
+
+		// Check for the right subtree
+		if (!isBSTBetter(cur.getRight())) {
+			return false;
+		}
+
+		return true;
+	}
+
+	public static void main(String[] args) {
+		BinarySearchTreeCheck btOne = new BinarySearchTreeCheck();
+		btOne.createBinaryTree(1);
+		BinarySearchTreeCheck btTwo = new BinarySearchTreeCheck();
+		btTwo.createBinaryTree(2);
+
+		// Only works if all the elements in the Binary Tree are unique.
+		System.out.println(btOne.isBSTBetter());
+		System.out.println(btTwo.isBSTBetter());
+	}
+}