class Solution {public:  vector<int> preorderTraversal(TreeNode *root) {    vector<int> out;    stack<TreeNode*> s;    s.push(root);    while(!s.empty() && root){      TreeNode *node = s.top();      out.push_back(node->val);      s.pop();      if(node->right) s.push(node->right);      if(node->left) s.push(node->left);    }    return out;  }  vector<int> inorderTraversal(TreeNode *root) {    stack<TreeNode *> s;    vector<int> out;    TreeNode *node = root;    bool done = false;    while(!done){      if(node){        s.push(node);        node = node->left;      }else {        if(s.empty()) done = true;        else{          node = s.top();          s.pop();          out.push_back(node->val);          node = node->right;        }      }    }    return out;  }  vector<int> postorderTraversal(TreeNode *root) {    vector<int> out;    stack<TreeNode*> s;    TreeNode* node = root;    s.push(node);    while(!s.empty()&&node){      node = s.top();      out.push_back(node->val);      s.pop();      if(node->left) s.push(node->left);      if(node->right)s.push(node->right);    }    reverse(out.begin(),out.end());    return out;  }};