Valid BST: refactoring + added unit test (#3883)
Co-authored-by: Debasish Biswas <debasishbsws.abc@gmail.com>
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package com.thealgorithms.datastructures.trees;
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/**
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* This code recursively validates whether given Binary Search Tree (BST) is balanced or not.
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* Trees with only distinct values are supported.
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* Key points:
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* 1. According to the definition of a BST, each node in a tree must be in range [min, max],
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* where 'min' and 'max' values represent the child nodes (left, right).
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* 2. The smallest possible node value is Integer.MIN_VALUE, the biggest - Integer.MAX_VALUE.
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*/
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public class ValidBSTOrNot {
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class Node {
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int data;
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Node left, right;
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public Node(int item) {
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data = item;
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left = right = null;
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}
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}
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// Root of the Binary Tree
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/* can give min and max value according to your code or
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can write a function to find min and max value of tree. */
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/* returns true if given search tree is binary
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search tree (efficient version) */
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boolean isBST(Node root) {
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public static boolean isBST(BinaryTree.Node root) {
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return isBSTUtil(root, Integer.MIN_VALUE, Integer.MAX_VALUE);
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}
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/* Returns true if the given tree is a BST and its
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values are >= min and <= max. */
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boolean isBSTUtil(Node node, int min, int max) {
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/* an empty tree is BST */
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private static boolean isBSTUtil(BinaryTree.Node node, int min, int max) {
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// empty tree is a BST
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if (node == null) {
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return true;
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}
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/* false if this node violates the min/max constraints */
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if (node.data < min || node.data > max) {
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return false;
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}
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/* otherwise check the subtrees recursively
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tightening the min/max constraints */
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// Allow only distinct values
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return (
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isBSTUtil(node.left, min, node.data - 1) &&
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isBSTUtil(node.right, node.data + 1, max)
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@ -0,0 +1,61 @@
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package com.thealgorithms.datastructures.trees;
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import org.junit.jupiter.api.Test;
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import static org.junit.jupiter.api.Assertions.assertFalse;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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/**
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* @author Albina Gimaletdinova on 17/02/2023
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*/
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public class ValidBSTOrNotTest {
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@Test
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public void testRootNull() {
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assertTrue(ValidBSTOrNot.isBST(null));
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}
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@Test
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public void testOneNode() {
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final BinaryTree.Node root = TreeTestUtils.createTree(new Integer[]{Integer.MIN_VALUE});
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assertTrue(ValidBSTOrNot.isBST(root));
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}
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/*
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9
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/ \
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7 13
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/\ / \
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3 8 10 20
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*/
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@Test
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public void testBinaryTreeIsBST() {
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final BinaryTree.Node root = TreeTestUtils.createTree(new Integer[]{9, 7, 13, 3, 8, 10, 20});
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assertTrue(ValidBSTOrNot.isBST(root));
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}
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/*
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9
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/ \
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7 13
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/\ / \
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3 8 10 13 <--- duplicated node
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*/
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@Test
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public void testBinaryTreeWithDuplicatedNodesIsNotBST() {
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final BinaryTree.Node root = TreeTestUtils.createTree(new Integer[]{9, 7, 13, 3, 8, 10, 13});
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assertFalse(ValidBSTOrNot.isBST(root));
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}
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/*
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9
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/ \
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7 13
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/\ / \
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3 8 10 12 <---- violates BST rule, needs to be more than 13 (parent node)
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*/
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@Test
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public void testBinaryTreeIsNotBST() {
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final BinaryTree.Node root = TreeTestUtils.createTree(new Integer[]{9, 7, 13, 3, 8, 10, 12});
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assertFalse(ValidBSTOrNot.isBST(root));
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}
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}
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