222.cpp

using namespace std;

struct TreeNode
{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode() : val(0), left(nullptr), right(nullptr) {}
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
};

class Solution
{
public:
    unsigned short int count = 0;

    int countNodes(TreeNode *root)
    {
        if (root == nullptr)
            return 0;

        return 1 + countNodes(root->left) + countNodes(root->right);
    }
};