struct node {    bool isfirst;    int val;    TreeNode* left,*right;    node(int _val,bool _isfirst){        val=_val;        isfirst=_isfirst;        this->left=this->right=NULL;    } };vector<int> postorderTraversal(TreeNode *root) {        // write your code here        vector<int> ret;        stack<node> sta;        TreeNode* p=root;        while(sta.size()>0||p)        {            while(p)            {                node n1(p->val,false);                n1.left=p->left;                n1.right=p->right;                sta.push(n1);                p=p->left;            }            if(sta.size()>0)            {                node tmp=sta.top();                sta.pop();                if(tmp.isfirst==false)                {                    tmp.isfirst=true;                    sta.push(tmp);                    p=tmp.right;                }                else                {                    ret.push_back(tmp.val);                    p=NULL;                }            }        }        return ret;    }

vector<int> preorderTraversal(TreeNode *root) {        // write your code here        vector<int> ret;        stack<TreeNode*> sta;        TreeNode* p=root;        while(sta.size()>0||p)        {            while(p)            {                sta.push(p);                ret.push_back(p->val);                p=p->left;            }            if(sta.size())            {                TreeNode* tmp=sta.top();                sta.pop();                p=tmp->right;            }        }        return ret;    }