力扣-144题（Java）-树的前序遍历（ArrayList）

逃离我推掉我的手 2022-10-16 07:20 148阅读 0赞

题目链接：[https://leetcode-cn.com/problems/binary-tree-preorder-traversal/][https_leetcode-cn.com_problems_binary-tree-preorder-traversal]  
题目如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70 1]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70 2]

/**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode() {}
     *     TreeNode(int val) { this.val = val; }
     *     TreeNode(int val, TreeNode left, TreeNode right) {
     *         this.val = val;
     *         this.left = left;
     *         this.right = right;
     *     }
     * }
     */
    class Solution {
        
        public List<Integer> preorderTraversal(TreeNode root) {
        
            List<Integer> array=new ArrayList<Integer>();
            preorder(root,array);//前序遍历：根——》左——》右
            return array;
        }
    
        public void preorder(TreeNode root,List<Integer> array){
        
            if(root==null) return;
    
            array.add(root.val);
            preorder(root.left,array);
            preorder(root.right,array);
        }
    }

[https_leetcode-cn.com_problems_binary-tree-preorder-traversal]: https://leetcode-cn.com/problems/binary-tree-preorder-traversal/
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70 2]: /images/20221014/5f0d3b570d0f4b0ea1097cb586eba142.png