[leetcode]145. Binary Tree Postorder Traversal@Java解题报告

https://leetcode.com/problems/binary-tree-postorder-traversal/description/

Given a binary tree, return the postorder traversal of its nodes' values.

For example:
Given binary tree {1,#,2,3},

   1    \     2    /   3

return [3,2,1].

Note: Recursive solution is trivial, could you do it iteratively?

package go.jacob.day810;import java.util.LinkedList;import java.util.List;import java.util.Stack;/** * 145. Binary Tree Postorder Traversal *  * @author Jacob * */public class Demo3 {public List<Integer> postorderTraversal(TreeNode root) {//用linkedList中addFirst方法比ArrayLisy效率更高LinkedList<Integer> res = new LinkedList<Integer>();Stack<TreeNode> stack1 = new Stack<TreeNode>();TreeNode node = root;while (!stack1.isEmpty() || node != null) {if (node == null) {node = stack1.pop();node = node.left;} else {stack1.push(node);res.addFirst(node.val);node = node.right;}}return res;}}