Untitled

class Solution
{
    public:
    //Function to return a list of nodes visible from the top view 
    //from left to right in Binary Tree.
    vector<int> topView(Node *root){
        //Your code here
        
        if(root == nullptr) return {};
        
        queue<pair<Node*, int>>q; // node line
        map<int,int> mp; // line node
        
        q.push( {root, 0} );
        
        while(!q.empty()){
            int sz = q.size();
            
            while(sz--){
                pair<Node*, int> curr = q.front();
                q.pop();
                
                int currNode = curr.first->data;
                int verticalLvl = curr.second;
                
                if(mp.find(verticalLvl) == mp.end()){
                    mp[verticalLvl] = currNode;
                }
                
                if(curr.first->left != nullptr){
                    q.push( {curr.first->left, verticalLvl-1 } );
                }

                if(curr.first->right != nullptr){
                    q.push( {curr.first->right, verticalLvl+1 } );
                }

            }        
        }
        
        vector<int>ans;
        
        for(auto &curr : mp){
            ans.push_back(curr.second);
        }
        
        return ans;
    }

};