Height of Special Binary Tree — C++

// Time:  O(n)
// Space: O(h)

// dfs
class Solution {
public:
    int heightOfTree(TreeNode* root) {
        int result = -1;
        vector<pair<TreeNode *, int>> stk = {{root, 0}};
        while (!empty(stk)) {
            const auto [u, d] = stk.back(); stk.pop_back();
            result = max(result, d);
            if (u->right && u->right->left != u) {
                stk.emplace_back(u->right, d + 1);
            }
            if (u->left && u->left->right != u) {
                stk.emplace_back(u->left, d + 1);
            }
        }
        return result;
    }
};

// Time:  O(n)
// Space: O(w)
// bfs
class Solution2 {
public:
    int heightOfTree(TreeNode* root) {
        int result = -1;
        vector<TreeNode *> q = {root};
        while (!empty(q)) {
            vector<TreeNode *> new_q;
            for (const auto& u : q) {
                if (u->left && u->left->right != u) {
                    new_q.emplace_back(u->left);
                }
                if (u->right && u->right->left != u) {
                    new_q.emplace_back(u->right);
                }
            }
            q = move(new_q);
            ++result;
        }
        return result;
    }
};