Leetcode #144 Binary Tree Preorder traversal

Title Link: https://leetcode.com/problems/binary-tree-preorder-traversal/

(Non-recursive implementation) the first order traversal of a binary tree.

1 classSolution2 {3  Public:4vector<int> Preordertraversal (TreeNode *root)5     {6vector<int>output;7         if(Root = =NULL)8         {9             returnoutput;Ten         } One  AStack<treenode*>Nodestack; - Nodestack.push (root); -  the          while(!nodestack.empty ()) -         { -TreeNode *topnode =nodestack.top (); -TreeNode *topleftnode = topnode->left, *toprightnode = topnode->Right ; +Output.push_back (topnode->val); -Nodestack.pop ();//first pop again push.  +              A             if(Toprightnode! = NULL)//because the last access to the right node, the right node is first pressed into the stack.  at Nodestack.push (toprightnode); -             if(Topleftnode! =NULL) - Nodestack.push (Topleftnode);  -         } -  -         returnoutput; in     } -};

Leetcode #144 Binary Tree Preorder traversal