Diameter of a Binary Tree

// C program to find the diameter
// of a binary tree.
#include <stdio.h>
#include <stdlib.h>

// Definition of a Node
struct Node {
    int data;
    struct Node* left;
    struct Node* right;
};

// Function to create a new Node
struct Node* newNode(int x) {
    struct Node* node = (struct Node*)malloc(sizeof(struct Node));
    node->data = x;
    node->left = NULL;
    node->right = NULL;
    return node;
}

int max (int a, int b) {
  	return a > b ? a : b;
}

// Recursive function which finds the 
// height of root and also calculates 
// the diameter of the tree.
int diameterRecur(struct Node* root, int* res) {

    // Base case: tree is empty
    if (root == NULL)
        return 0;

    // find the height of left and right subtree
    // (it will also find of diameter for left 
    // and right subtree).
    int lHeight = diameterRecur(root->left, res);
    int rHeight = diameterRecur(root->right, res);

    // Check if diameter of root is greater
    // than res.
    *res = max(*res , lHeight + rHeight);

    // return the height of current subtree.
    return 1 + max(lHeight, rHeight);
}

// Function to get diameter of a binary tree
int diameter(struct Node* root) {

    int res = 0;
    diameterRecur(root, &res);
    return res;
}

int main() {

    // Constructed binary tree is
    //          5
    //        /   \
    //       8     6
    //      / \   /
    //     3   7 9
    struct Node* root = newNode(5);
    root->left = newNode(8);
    root->right = newNode(6);
    root->left->left = newNode(3);
    root->left->right = newNode(7);
    root->right->left = newNode(9);

    printf("%d\n", diameter(root));

    return 0;
}