# Finding Mode in a Binary Search Tree in JavaScript

## Mode:

Mode of a set of data is simply the number that occurs for most number of times in that set of data. For instance, 3 is the mode of dataset 2, 3, 1, 3, 4, 2, 3, 1 as it occurs for most number of times.

## Binary Search Tree

A tree DS is a valid Binary Search Tree if it fulfils the following conditions −

• The left subtree of a node contains only nodes with keys less than or equal to the node's key.

• The right subtree of a node contains only nodes with keys greater than or equal to the node's key.

• Both the left and right subtrees must also be binary search trees.

## Problem

We are required to write a JavaScript function that takes in a BST root as the only argument. The BST may or most probably contain duplicates. We are required to find and return the mode of the data stored by the tree.

## 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(1);
BST.insert(3);
BST.insert(3);
BST.insert(2);
BST.insert(3);
BST.insert(2);
const findMode = function(root) {
let max = 1;
const hash = {};
const result = [];
const traverse = node => {
if (hash[node.data]) {
hash[node.data] += 1;
max = Math.max(max, hash[node.data]);
} else {
hash[node.data] = 1;
};
node.left && traverse(node.left);
node.right && traverse(node.right);
};
if(root){
traverse(root);
};
for(const key in hash) {
hash[key] === max && result.push(key);
};
return +result[0];
};
console.log(findMode(BST.root));

## Output

And the output in the console will be −

3

Updated on: 04-Mar-2021

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