题目
描述
给出一棵二叉树，返回其节点值的前序遍历。
样例
给出一棵二叉树 {1,#,2,3},
1 \ 2 / 3
返回 [1,2,3].
解答
思路
前序遍历二叉树
代码
/**
* Definition of TreeNode:
* public class TreeNode {
* public int val;
* public TreeNode left, right;
* public TreeNode(int val) {
* this.val = val;
* this.left = this.right = null;
* }
* }
*/
public class Solution {
/**
* @param root: The root of binary tree.
* @return: Preorder in ArrayList which contains node values.
*/
public ArrayList<Integer> preorderTraversal(TreeNode root) {
// write your code here
ArrayList<Integer> a = new ArrayList<Integer>();
preOrder(a, root);
return a;
}
private void preOrder(ArrayList<Integer> a, TreeNode root){
if(root == null) return;
a.add(root.val);
preOrder(a, root.left);
preOrder(a, root.right);
}
}
