题解 | #二叉树的后序遍历#
二叉树的后序遍历
https://www.nowcoder.com/practice/1291064f4d5d4bdeaefbf0dd47d78541
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[] postorderTraversal (TreeNode root) { // write code here List<Integer> list = new ArrayList(); Stack<TreeNode> stack = new Stack<>(); TreeNode pre = null; while(root != null || !stack.isEmpty()){ while(root!=null){ stack.push(root); root = root.left; } root = stack.pop(); if(root.right==null || pre == root.right){ list.add(root.val); pre = root; root = null; }else{ stack.push(root); root = root.right; } } int[] res = new int[list.size()]; for(int i = 0; i < list.size(); i++){ res[i] = list.get(i); } return res; } }