Diameter of a Binary Tree

//{ Driver Code Starts
#include <bits/stdc++.h>
using namespace std;

/* A binary tree node has data, pointer to left child
   and a pointer to right child */
struct Node {
    int data;
    struct Node* left;
    struct Node* right;
};
Node* newNode(int val) {
    Node* temp = new Node;
    temp->data = val;
    temp->left = NULL;
    temp->right = NULL;
    return temp;
}
Node* buildTree(string str) {
    // Corner Case
    if (str.length() == 0 || str[0] == 'N') return NULL;

    // Creating vector of strings from input
    // string after spliting by space
    vector<string> ip;

    istringstream iss(str);
    for (string str; iss >> str;) ip.push_back(str);

    // Create the root of the tree
    Node* root = newNode(stoi(ip[0]));

    // Push the root to the queue
    queue<Node*> queue;
    queue.push(root);

    // Starting from the second element
    int i = 1;
    while (!queue.empty() && i < ip.size()) {

        // Get and remove the front of the queue
        Node* currNode = queue.front();
        queue.pop();

        // Get the current node's value from the string
        string currVal = ip[i];

        // If the left child is not null
        if (currVal != "N") {

            // Create the left child for the current node
            currNode->left = newNode(stoi(currVal));

            // Push it to the queue
            queue.push(currNode->left);
        }

        // For the right child
        i++;
        if (i >= ip.size()) break;
        currVal = ip[i];

        // If the right child is not null
        if (currVal != "N") {

            // Create the right child for the current node
            currNode->right = newNode(stoi(currVal));

            // Push it to the queue
            queue.push(currNode->right);
        }
        i++;
    }

    return root;
}


// } Driver Code Ends
/* Tree node structure  used in the program

struct Node
{
    int data;
    struct Node* left;
    struct Node* right;

    Node(int x){
        data = x;
        left = right = NULL;
    }
}; */

class Solution {
    private:
    
    int height(Node* node)
    {
        if(node == NULL)
        {
            return 0;
        }
        
        int left = height(node -> left);
        
        int right = height(node -> right);
        
        int ans = max(left , right) + 1;
        
        
        return ans;
    }
    
    pair<int, int> diameterFast(Node* root)
    {
        if(root == NULL)
        {
            pair<int, int> p = make_pair(0, 0);
            return p;
        }
        
        pair<int, int> left = diameterFast( root -> left);
        pair<int, int> right = diameterFast(root -> right);
        
        int leftAns = left.first;
        int rightAns = right.first;
        
        int combo = left.second + right.second + 1;
        
        pair<int, int> ans;
        
        //it holds the diameter of the subtree
        ans.first = max(leftAns, max(rightAns, combo));
        
        //it holds the height of the subtree
        ans.second = max(left.second, right.second) + 1;
        
        
        return ans;
    }
    
    public:
    // Function to return the diameter of a Binary Tree.
    
    int diameter(Node* root) {
        // if(root == NULL)
        // {
        //     return 0;
        // }
        
        // int left = diameter(root -> left);
        // int right = diameter(root -> right);
        
        // int combo = height(root -> left) + height(root -> right) + 1;
        
        // return max(left, max(right, combo));
        
        return diameterFast(root).first;
    }
};

//{ Driver Code Starts.

/* Driver program to test size function*/
int main() {
    int t;
    scanf("%d\n", &t);
    while (t--) {
        string s;
        getline(cin, s);
        Node* root = buildTree(s);
        Solution ob;
        cout << ob.diameter(root) << endl;
    }
    return 0;
}

// } Driver Code Ends