Leetcode 623. Add One Row to Tree

https://leetcode.com/problems/add-one-row-to-tree/description/

class Solution {
public:
    TreeNode* addOneRow(TreeNode* root, int v, int d) {
        
        if (d == 1) {
            TreeNode* ret = new TreeNode(v);
            ret->left = root;
            return ret;
        }
        
        
        queue< pair<TreeNode*, int> > q;
        q.push( make_pair(root, 2) );
        while (!q.empty()) {
            pair<TreeNode*, int> tp = q.front();
            q.pop();
            if (tp.second == d) {
                TreeNode* tmp = tp.first->left;
                tp.first->left = new TreeNode(v);
                tp.first->left->left = tmp;
                tmp = tp.first->right;
                tp.first->right = new TreeNode(v);
                tp.first->right->right = tmp;
                continue;
            }
            
            if (tp.second + 1 <= d) {
                if (tp.first->left) {
                    q.push( make_pair(tp.first->left, tp.second + 1) );
                }
                if (tp.first->right) {
                    q.push( make_pair(tp.first->right, tp.second + 1) );
                }
                
            }
            
        }
        return root;
    } 
};