void topView(Node * root) {
        map<int,int>i;
        queue<pair<Node*,int>>q;q.push({root,500});
        while(!q.empty()){
            pair<Node*,int> t=q.front();q.pop();
            if(t.first->left)q.push({t.first->left,t.second-1});
            if(t.first->right)q.push({t.first->right,t.second+1});
            if(!i[t.second])i[t.second]=t.first->data;
        }
        for(auto k:i)cout<<k.second<<" ";
    }