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CheckBSTOrNot.java
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package binarySearchTree1;
import static binarySearchTree1.SearchInBST.levelWiseInput;
class IsBSTReturn {
int minimum;
int maximum;
boolean isBST;
public IsBSTReturn(int minimum, int maximum, boolean isBST) {
this.minimum = minimum;
this.maximum = maximum;
this.isBST = isBST;
}
}
public class CheckBSTOrNot {
public static boolean checkBST(TreeNode<Integer> root) {
if (root == null) return true;
int leftMax = maximum(root.left);
if (leftMax >= root.data) {
return false;
}
int rightMin = minimum(root.right);
if (rightMin < root.data) {
return false;
}
return checkBST(root.left) && checkBST(root.right);
}
private static int minimum(TreeNode<Integer> root) {
if (root == null) return Integer.MAX_VALUE;
int left = minimum(root.left);
int right = minimum(root.right);
return Math.min(root.data, Math.min(left, right));
}
private static int maximum(TreeNode<Integer> root) {
if (root == null) return Integer.MIN_VALUE;
int left = maximum(root.left);
int right = maximum(root.right);
return Math.max(root.data, Math.max(left, right));
}
public static IsBSTReturn isBSTImproved(TreeNode<Integer> root) {
if (root == null) {
return new IsBSTReturn(Integer.MAX_VALUE, Integer.MIN_VALUE, true);
}
var left = isBSTImproved(root.left);
var right = isBSTImproved(root.right);
int minimum = Math.min(root.data, Math.min(left.minimum, right.minimum));
int maximum = Math.max(root.data, Math.max(left.maximum, right.maximum));
boolean isBST = left.maximum < root.data || right.minimum >= root.data || left.isBST || right.isBST;
return new IsBSTReturn(minimum, maximum, isBST);
}
public static void main(String[] args) {
var root = levelWiseInput();
// System.out.println(checkBST(root));
System.out.println(isBSTImproved(root).isBST);
}
}