LeetCode 144. Binary Tree Preorder Traversal solution report

LeetCode 144. Binary Tree Preorder Traversal solution report
144. Binary Tree Preorder TraversalMy SubmissionsQuestionTotal Accepted: 108336 Total Submissions: 278322 Difficulty: Medium

Given a binary tree, return thepreordertraversal of its nodes 'values.

For example:
Given binary tree{1,#,2,3},

   1    \     2    /   3

Return[1,2,3].

Note: Recursive solution is trivial, cocould you do it iteratively?

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Returns the first root traversal order of a binary tree. The recursive solution is very simple. Can it be solved in a non-recursive way.

When traversing a node, the right child is added to the stack. Search left until it is empty.

My AC code

public class BinaryTreePreorderTraversal {public List
 
   preorderTraversal(TreeNode root) {        List
  
    list = new ArrayList
   
    ();        Stack
    
      stack = new Stack
     
      ();        TreeNode cur = root;        while (cur != null || !stack.isEmpty()) {while (cur != null) {list.add(cur.val);if(cur.right != null) stack.add(cur.right);cur = cur.left;}if(!stack.isEmpty()) cur = stack.pop();}        return list;    }}