非递归的方式后序遍历二叉树

来源：互联网发布：镜之边缘催化剂优化编辑：程序博客网时间：2024/06/06 15:38

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */import java.util.*;public class Solution {    public ArrayList<Integer> postorderTraversal(TreeNode root) {        ArrayList<Integer> als = new ArrayList<Integer>();        if(root == null){            return als;        }        Stack<TreeNode> s1 = new Stack<TreeNode>();        Stack<TreeNode> s2 = new Stack<TreeNode>();        TreeNode iter = root;        s1.push(iter);        while(!s1.isEmpty()){            TreeNode head = s1.pop();            s2.push(head);            if(head.left != null){                s1.push(head.left);            }            if(head.right != null){                s1.push(head.right);            }        }        while(!s2.isEmpty()){            als.add(s2.pop().val);        }        return als;    }}

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