1. Check you current version on terminal

node --version

2. Install NVM , it is a Node Version Manager. In below link scroll down to

nvm-setup.exe to install .

Releases · coreybutler/nvm-windows

You can assure the installation by checking

nvm --version

3. Now lets say you want to install 14.0.0 version of node. Go back to terminal and type:

nvm install 14.0.0

4. Type the below command to check the versions you have :

nvm list

The output will contain the previous version of node and the one you installed in the last step.

5. Using the step 3 you can install as many version as you want. Now to use a particular version: type: nvm use version

nvm use 14.0.0

To check the current node version use node — — version , this time it will show 14.0.0.

Given a Binary Tree of size N, your task is to return the sum of all the nodes of the given binary tree.

Declare globally :

    int sum=0;
    int SumBST(TreeNode* root ) {
        
        if( !root ) return 0;
        
        sum += root->val;
        // cout<<sum<<" ";      
       
        SumBST(root->left);
        SumBST(root->right);
         
        
        return sum;
    }

anything you want to return from the recursive function , just declare the variable globally. Here the variable is sum,

sum += root->val

will keep accumulating the values returned from the recursive calls.

SumBST(root->left );
SumBST(root->right );

Modify the Function arguments:

    void dfs(TreeNode* root, int& sum){
        if(!root) return ;
        sum+=root->val;
        dfs(root->left,sum);
        dfs(root->right,sum);
    }

    int SumBST(TreeNode* root ) {
        
        int sum =0;
        dfs(root,sum);
        return sum;
    }

You must have seen this very often. Many of us modify the original function arguments, which can be hard to draw to visualize. I will suggest you to make a different function for such cases.

Here the dfs function have an additional argument sum ,

which will collect all the node values

sum+=root->val;

obtained from recursive calls

dfs(root->left ,sum);
dfs(root->right, sum);

A systematic way:

    int SumBST(TreeNode* root ) {
        
        if( !root ) return 0;
        
        int sum =0;
        sum += root->val;
        // cout<<sum<<" ";      
       
        sum += SumBST(root->left);
        sum += SumBST(root->right);
         
        
        return sum;
    }

In case the Interviewer ask you to not declare the variable globally and to not to modify the arguments, you can just simply write our little variable inside the function and gather the values in sum using

sum += SumBST(root->left);
sum += SumBST(root->right);

with the base condition

if(root) sum += root->val;

I hope that helps. Lemme know in comment section , If I can add something .