题解 | #二叉树的前序遍历#
二叉树的前序遍历
https://www.nowcoder.com/practice/5e2135f4d2b14eb8a5b06fab4c938635
import java.util.*; /* * public class TreeNode { * int val = 0; * TreeNode left = null; * TreeNode right = null; * public TreeNode(int val) { * this.val = val; * } * } */ public class Solution { /** * 代码中的类名、方法名、参数名已经指定,请勿修改,直接返回方法规定的值即可 * * * @param root TreeNode类 * @return int整型一维数组 */ public int[] preorderTraversal (TreeNode root) { // write code here ArrayList<Integer> arr = new ArrayList<Integer>(); if(root != null){ arr.add(root.val); if(root.left != null){ travel(root.left, arr); } if(root.right != null){ travel(root.right, arr); } } int[] arrInt = new int[arr.size()]; for(int i = 0; i < arrInt.length; i++){ arrInt[i] = arr.get(i); } return arrInt; } public void travel(TreeNode root, ArrayList<Integer> arr){ if(root != null){ arr.add(root.val); } if(root.left != null){ travel(root.left, arr); } if(root.right != null){ travel(root.right, arr); } } }