Leetcode(144) Binary Tree Preorder Traversal

发表于 | 分类于

Description:

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

解法：

递归解题，具体代码如下：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

class Solution {
    public List<Integer> preorderTraversal(TreeNode root) {
        List<Integer> output = new ArrayList();
        helper(root,output);
        return output;
    }
    void helper(TreeNode root,List<Integer> output){
        if(root == null){
            return;
        }
        output.add(root.val);
        helper(root.left,output);
        helper(root.right,output);
    }
}