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BST_CheckForBST.java
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BST_CheckForBST.java
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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.LinkedList;
import java.util.Queue;
// https://practice.geeksforgeeks.org/problems/check-for-bst/1
// https://www.youtube.com/watch?v=MILxfAbIhrE
// https://www.geeksforgeeks.org/a-program-to-check-if-a-binary-tree-is-bst-or-not/
public class BST_CheckForBST {
private static boolean isBST(Node root, int lowerLimit, int upperLimit) {
if(root == null) return true;
if((lowerLimit < root.data) && (root.data < upperLimit)) {
if(isBST(root.left, lowerLimit, root.data) && isBST(root.right, root.data, upperLimit)) {
return true;
}
}
return false;
}
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int t = Integer.parseInt(br.readLine());
while(t-->0) {
String ip = br.readLine().trim();
Node root = buildTree(ip);
System.out.println(isBST(root, Integer.MIN_VALUE, Integer.MAX_VALUE)? "1" : "0");
}
}
private static Node buildTree(String str) {
if(str.length()==0 || str.charAt(0)=='N') {
return null;
}
String ip[] = str.split("\\s+");
Node root = new Node(Integer.parseInt(ip[0]));
Queue<Node> queue = new LinkedList<>();
queue.add(root);
int i = 1;
while(queue.size() > 0 && i < ip.length) {
Node currNode = queue.peek();
queue.remove();
String currVal = ip[i];
if (!currVal.equals("N")) {
currNode.left = new Node(Integer.parseInt(currVal));
queue.add(currNode.left);
}
i++;
if(i >= ip.length) break;
currVal = ip[i];
if(!currVal.equals("N")) {
currNode.right = new Node(Integer.parseInt(currVal));
queue.add(currNode.right);
}
i++;
}
return root;
}
private static class Node {
private int data;
private Node left;
private Node right;
Node(int data) {
this.data = data;
this.left = this.right = null;
}
}
}