LeetCode : Binary Tree Postorder Traversal

 vector<int> postorderTraversal(TreeNode *root) {
        vector<TreeNode *> vec;
        vector<int > vecResult;
        TreeNode *pointer=root;
 
	while (pointer)
	{
		while (pointer->left)
		{
			vec.push(pointer);
			pointer=pointer->left;
		}
		while (pointer->right==NULL||(pointer->right==pre))
		{
			pre=pointer;  
vecResult.push_back(pointer->val); 			if(vec.empty()){
			
				return vecResult;
			}
			pointer=stackNode.top();
			stackNode.pop();
		}

		vec.push(pointer);
		pointer=pointer->right;        return vecResult;
}    }