94. 二叉树的中序遍历

class Solution {
public:
    vector inorderTraversal(TreeNode* root) {
        vector ans;
        
        stack S;
        TreeNode *p=root;
        while(p || !S.empty() ){
            if(p){
                cout<<1;
                S.push(p);
                p=p->left;
            }        
            else{
                p=S.top();
                ans.push_back(p->val);
                S.pop();
                
                p=p->right;
            }

        }

        return ans;
    }
};