[leetcode]Binary Tree Postorder Traversal

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[leetcode]Binary Tree Postorder Traversal

Binary Tree Postorder Traversal

 

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].

 后序遍历，题中提示说不让用递归，让用迭代。明天再搞吧。

 

先给出一个递归版本：

	ArrayList<Integer> result = new ArrayList<Integer>();
    public ArrayList<Integer> postorderTraversal(TreeNode root) {
        if(root == null){
        	return result;
        }
        postOrder(root);
        return result;
    }
    private void postOrder(TreeNode root){
    	if(root.left != null){
        	postorderTraversal(root.left);
        }
        if(root.right != null){
        	postorderTraversal(root.right);
        }
        result.add(root.val);
    }