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].
代码如下：
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<Integer> preorderTraversal(TreeNode root) {
List<Integer> list=new ArrayList<>();
if(root==null)
return list; list.add(root.val); if(root.left!=null)
list.addAll(preorderTraversal(root.left));
if(root.right!=null)
list.addAll(preorderTraversal(root.right)); return list;
}
}