(java)Binary Tree Preorder Traversal

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]

.

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

思路:就是一个先序遍历

代码如下(已通过leetcode)

public class Solution {

List<Integer> list=new ArrayList<Integer>();

public List<Integer> preorderTraversal(TreeNode root) {

if(root==null) return list;

list.add(root.val);

if(root.left!=null) preorderTraversal(root.left);

if(root.right!=null) preorderTraversal(root.right);

return list;

}

}