# Checking for univalued Binary Search Tree in JavaScript

## Univalued Binary Search Tree

A binary search tree is univalued if every node in the tree has the same value.

## Problem

We are required to write a JavaScript function that takes in the root of a BST and returns true if and only if the given tree is univalued, false otherwise.

For example, if the nodes of the tree are −

const input = [5, 5, 5, 3, 5, 6];

Then the output should be −

const output = false;

## Example

The code for this will be −

Live Demo

class Node{
constructor(data) {
this.data = data;
this.left = null;
this.right = null;
};
};
class BinarySearchTree{
constructor(){
// root of a binary seach tree
this.root = null;
}
insert(data){
var newNode = new Node(data);
if(this.root === null){
this.root = newNode;
}else{
this.insertNode(this.root, newNode);
};
};
insertNode(node, newNode){
if(newNode.data < node.data){
if(node.left === null){
node.left = newNode;
}else{
this.insertNode(node.left, newNode);
};
} else {
if(node.right === null){
node.right = newNode;
}else{
this.insertNode(node.right,newNode);
};
};
};
};
const BST = new BinarySearchTree();
BST.insert(5);
BST.insert(5);
BST.insert(5);
BST.insert(3);
BST.insert(5);
BST.insert(6);
const isUnivalued = (root) => {
const helper = (node, prev) => {
if (!node) {
return true
}
if (node.data !== prev) {
return false
}
let isLeftValid = true
let isRightValid = true
if (node.left) {
isLeftValid = helper(node.left, prev)
}
if (isLeftValid && node.right) {
isRightValid = helper(node.right, prev)
}
return isLeftValid && isRightValid
}
if (!root) {
return true
}
return helper(root, root.data)
};
console.log(isUnivalued(BST.root));

## Output

And the output in the console will be −

false