leetcode 145. 二叉树的后序遍历

 1 //递归算法
 2 class Solution {
 3     public List<Integer> postorderTraversal(TreeNode root) {
 4         List<Integer> list = new ArrayList<Integer>();
 5         if(root==null) return list;
 6         postorder(root,list);
 7         return list;
 8     }
 9     public List<Integer> postorder(TreeNode node,List<Integer> list){
10         if(node.left!=null)postorder(node.left,list);
11         if(node.right!=null)postorder(node.right,list);
12         list.add(node.val);
13         return list;
14     }
15 }
16 //迭代算法
17 class Solution {
18     public List<Integer> postorderTraversal(TreeNode root) {
19         List<Integer> list = new ArrayList<Integer>();
20         if(root==null)return list;
21         Stack<TreeNode> stack = new Stack<TreeNode>();
22         Stack<TreeNode> stackresult = new Stack<TreeNode>();
23         stack.push(root);
24         while(!stack.empty()){
25             TreeNode tmpnode = stack.pop();
26             stackresult.push(tmpnode);
27             if(tmpnode.left!=null)stack.push(tmpnode.left);
28             if(tmpnode.right!=null)stack.push(tmpnode.right);
29         }
30         while(!stackresult.empty()){
31             TreeNode tmpnode = stackresult.pop();
32             list.add(tmpnode.val);
33         }
34         return list;
35     }
36 }