Shortest Range In BST

class Solution{
    
    public:
   int findDepth(Node *root)
    {
        if(root==NULL)
        return 0;
        return 1 + max(findDepth(root->left), findDepth(root->right));
        
    }
    pair<int, int> shortestRange(Node *root) {
        // Your code goes here
        queue<Node*> q;
        q.push(root);
        int l = root->data, r = root->data;
        int d = findDepth(root);
        
        vector<vector<int>> nums(d);
        int i = 0 ;
        while(!q.empty())
        {
            int size = q.size();
   
            
            
            while(size--)
            {
            
                Node* x = q.front();
                q.pop();
                nums[i].push_back(x->data);
                
                if(x->left)
                q.push(x->left);
                if(x->right)
                q.push(x->right);
                
            }
         ++i;
         
        }
     
        pair<int, int> ans;
        int gap = INT_MAX;
        set<pair<int, pair<int, int>>> st;
        for (int i = 0; i < nums.size(); ++i)
        {
            st.insert({nums[i][0], {i, 0}});
        }
        while (1)
        {
            pair<int, pair<int, int>> mini = *st.begin();
            auto it = st.end();
            --it;
            pair<int, pair<int, int>> maxi = *it;

            st.erase(st.begin());
            if (maxi.first - mini.first < gap)
            {
                gap = maxi.first - mini.first;
                ans.first = mini.first;
                ans.second = maxi.first;
            }
            if (mini.second.second + 1 >= nums[mini.second.first].size())
                break;
            st.insert({nums[mini.second.first][mini.second.second + 1], {mini.second.first, mini.second.second + 1}});
            
        }
        return ans;
    }
 
};