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package trees.binarySearchTree;
// Problem Title => Check if a tree is a BST or not
public class Problem_5 {
static class Node {
int data;
Node left, right;
public Node(int item) {
data = item;
left = right = null;
}
}
Node root;
/*
* can give min and max value according to your code or can write a function to
* find min and max value of tree.
*/
/*
* returns true if given search tree is binary search tree (efficient version)
*/
boolean isBST() {
return isBSTUtil(root, Integer.MIN_VALUE, Integer.MAX_VALUE);
}
/*
* Returns true if the given tree is a BST and its values are >= min and <= max.
*/
boolean isBSTUtil(Node node, int min, int max) {
/* an empty tree is BST */
if (node == null)
return true;
/* false if this node violates the min/max constraints */
if (node.data < min || node.data > max)
return false;
/*
* otherwise check the subtrees recursively tightening the min/max constraints
*/
// Allow only distinct values
return (isBSTUtil(node.left, min, node.data - 1) && isBSTUtil(node.right, node.data + 1, max));
}
public static void main(String[] args) {
Problem_5 tree = new Problem_5();
tree.root = new Node(4);
tree.root.left = new Node(2);
tree.root.right = new Node(5);
tree.root.left.left = new Node(1);
tree.root.left.right = new Node(3);
if (tree.isBST())
System.out.println("IS BST");
else
System.out.println("Not a BST");
}
}