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]
.
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<Integer> preorderTraversal(TreeNode root) {
preOrder(root);
return list;
}
public List<Integer> list = new ArrayList<Integer>();
public void preOrder(TreeNode root){
if(root == null)return;
list.add(root.val);
preOrder(root.left);
preOrder(root.right);
}
}