class Solution {
public:
    vector<int> inorderTraversal(TreeNode *root) {
        vector<int>result;
        stack<TreeNode*>st;
        TreeNode*p=root;
        while(!st.empty()||p)
        {
            if(p)
            {
                st.push(p),p=p->left;
            }
            else
            {
                p=st.top();
                st.pop();
                result.push_back(p->val);
                p=p->right;
            }
        }
        return result;
    }
};