LeetCode "Binary Tree Right Side View"

class Solution {
public:
    typedef pair<TreeNode*, int> Rec;
    vector<int> rightSideView(TreeNode *root) 
    {
        vector<int> v;
        if (!root) return v;

        stack<Rec> stk;        
        //
        int max_d = 0;
        TreeNode *p = root;
        while (p)
        {
            stk.push(Rec(p, ++max_d));
            v.push_back(p->val);
            
            p = p->right;
        }

        //        
        while (!stk.empty())
        {
            Rec p0 = stk.top(); stk.pop();
        
            if (p0.first->left)
            {
                TreeNode *pl = p0.first->left;
                int myd = p0.second;

                while (pl)
                {
                    stk.push(Rec(pl, ++ myd));
                    if (myd > max_d)
                    {
                        v.push_back(pl->val);
                        max_d = myd;
                    }
                    pl = pl->right;
                }
            }// if
        }
        return v;
    }
};