LeetCode 二叉樹的前序遍歷 java
阿新 • • 發佈:2019-01-29
給定一個二叉樹,返回它的 前序 遍歷。
示例:
輸入: [1,null,2,3] 1 \ 2 / 3 輸出: [1,2,3]
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public List<Integer> preorderTraversal(TreeNode root) { List<Integer> resultList = new ArrayList<>(); if(root == null){ return resultList; } helper(resultList,root); return resultList; } public void helper(List<Integer> resultList,TreeNode root){ if(root==null) return; resultList.add(root.val); helper(resultList,root.left); helper(resultList,root.right); } }