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;
  }
};