LeetCode144 Binary Tree PreOrder Traversal Java question (recursive iteration)

LeetCode144 Binary Tree PreOrder Traversal Java question (recursive iteration)

Question:

 

Given a binary tree, return the preorder traversal of its nodes 'values.

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

   1         2    /   3

 

Return[1,2,3].

Solution:

The idea of traversing a binary tree in sequence is similar to that in the previous article. Just give it to the code.

 

Recursion:

 

public static List
 
   reslut=new ArrayList<>();public static  List
  
    preorderTraversal(TreeNode root) {if(root!=null) {reslut.add(root.val);preorderTraversal(root.left);preorderTraversal(root.right);}return reslut;         }
  
 

Iteration:

 

 

public static  List
 
   preorderTraversal2(TreeNode root) {List
  
    res=new ArrayList<>();Stack
   
     nodeStack=new Stack<>();while(true){while(root!=null){res.add(root.val);nodeStack.push(root);root=root.left;}if(nodeStack.isEmpty()) break;TreeNode tempNode=nodeStack.pop();root=tempNode.right;}return res;         }