Binary Tree Postorder Traversal

iterative_postorder_traversal.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> postorderTraversal(TreeNode* root) {
                vector<int> out;
        vector<TreeNode*> nodes;
        TreeNode* node;
        if (root != NULL)
            node = root;
        
        while(node != NULL)
        {
            if(node->left != NULL)
            {
                TreeNode* node_no_left = new TreeNode(node->val);
                if (node->right != NULL)
                    node_no_left->right = node->right;
                nodes.push_back(node_no_left);
                nodes.push_back(node->left);
            }        
            else
            {
                if(node->right != NULL)
                {
                    TreeNode* node_no_left = new TreeNode(node->val);
                    nodes.push_back(node_no_left);
                    nodes.push_back(node->right);
                }
                else
                {
                    out.push_back(node->val);
                }
            }
            
            if (nodes.empty())
                return out;
            else
            {
                node = nodes.back();
                nodes.pop_back();
            }
        }
        
        return out;
    }
};