leetcode 1145. Binary Tree Postorder Traversal ----- java

標籤：sem   init   integer   etc   return   arraylist   int   遞迴   post   

 

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?

 

求後序遍曆，要求不使用遞迴。

 

使用棧，從後向前添加。

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public List<Integer> postorderTraversal(TreeNode root) {        List list = new ArrayList<Integer>();                if( root == null )            return list;        Stack<TreeNode> stack = new Stack<TreeNode>();        stack.push(root);        while( !stack.isEmpty() ){            TreeNode node = stack.pop();            list.add(0,node.val);            if( node.left != null )                stack.push(node.left);            if( node.right != null )                stack.push(node.right);                    }        return list;    }}

 

leetcode 1145. Binary Tree Postorder Traversal ----- java