94.cpp

class Solution {
    vector<int> inorder;

public:
    vector<int> inorderTraversal(TreeNode* root) {
        stack<TreeNode*> st;
        while (1) {
            while (root != nullptr) {
                st.push(root);
                root = root->left;
            }
            if (st.empty())
                break;
            root = st.top();
            st.pop();
            inorder.push_back(root->val);
            root = root->right;
        }
        return inorder;
    }
};
class SolutionDFS {
    void impl(vector<int>& res, TreeNode* node) {
        if (!node)
            return;
        if (node->left) {
            impl(res, node->left);
        }
        res.push_back(node->val);
        if (node->right) {
            impl(res, node->right);
        }
    }

public:
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> res;
        impl(res, root);
        return res;
    }
};