222.cpp

/**
 * Definition for a binary tree node.
 * 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) {}
 * };
 */
#include <bits/stdc++.h>
#include <gtest/gtest.h>
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:
    int countNodes(TreeNode *root)
    {
        if (root == nullptr) {
            return 0;
        }
        return 1 + countNodes(root->left) + countNodes(root->right);
    }
};

// Helper function to delete a tree and free memory
void deleteTree(TreeNode *root)
{
    if (root == nullptr)
        return;
    deleteTree(root->left);
    deleteTree(root->right);
    delete root;
}

// Test cases
TEST(SolutionTest, EmptyTree)
{
    Solution sol;
    TreeNode *root = nullptr;
    EXPECT_EQ(sol.countNodes(root), 0);
}

TEST(SolutionTest, SingleNodeTree)
{
    Solution sol;
    TreeNode *root = new TreeNode(1);
    EXPECT_EQ(sol.countNodes(root), 1);
    deleteTree(root);
}

TEST(SolutionTest, LeftSkewedTree)
{
    Solution sol;
    // Tree: 1 -> 2 -> 3 (left-skewed)
    TreeNode *root =
        new TreeNode(1, new TreeNode(2, new TreeNode(3), nullptr), nullptr);
    EXPECT_EQ(sol.countNodes(root), 3);
    deleteTree(root);
}

TEST(SolutionTest, RightSkewedTree)
{
    Solution sol;
    // Tree: 1 -> 2 -> 3 (right-skewed)
    TreeNode *root =
        new TreeNode(1, nullptr, new TreeNode(2, nullptr, new TreeNode(3)));
    EXPECT_EQ(sol.countNodes(root), 3);
    deleteTree(root);
}

TEST(SolutionTest, CompleteBinaryTree)
{
    Solution sol;
    // Tree:
    //       1
    //     /   \
    //    2     3
    //   / \   /
    //  4   5 6
    TreeNode *root =
        new TreeNode(1, new TreeNode(2, new TreeNode(4), new TreeNode(5)),
                     new TreeNode(3, new TreeNode(6), nullptr));
    EXPECT_EQ(sol.countNodes(root), 6);
    deleteTree(root);
}

TEST(SolutionTest, FullBinaryTree)
{
    Solution sol;
    // Tree:
    //       1
    //     /   \
    //    2     3
    //   / \   / \
    //  4   5 6   7
    TreeNode *root =
        new TreeNode(1, new TreeNode(2, new TreeNode(4), new TreeNode(5)),
                     new TreeNode(3, new TreeNode(6), new TreeNode(7)));
    EXPECT_EQ(sol.countNodes(root), 7);
    deleteTree(root);
}

TEST(SolutionTest, UnbalancedTree)
{
    Solution sol;
    // Tree:
    //        1
    //       /
    //      2
    //     / \
    //    3   4
    //       /
    //      5
    TreeNode *root =
        new TreeNode(1,
                     new TreeNode(2, new TreeNode(3),
                                  new TreeNode(4, new TreeNode(5), nullptr)),
                     nullptr);
    EXPECT_EQ(sol.countNodes(root), 5);
    deleteTree(root);
}

int main(int argc, char **argv)
{
    testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}