【leetcode】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].

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

 

class Solution {
public:
    vector<int> postorderTraversal(TreeNode *root) {
        vector<int> out;
        stack<TreeNode*> s;
        TreeNode* node=root;
        s.push(node);
        while(!s.empty()&&node){
            node=s.top();
            out.push_back(node->val);
            s.pop();
            if(node->left) s.push(node->left);
            if(node->right) s.push(node->right);
        }
        
        reverse(out.begin(),out.end());
        return out;
    }
};