vector<vector<int> > Solution::verticalOrderTraversal(TreeNode* root) {
    unordered_map<int,vector<int>> mp;
    int mn = 0,mx = 0;
    queue<pair<TreeNode*,int>> q;
    if(!root) return {};
    q.push({root,0});
    while(q.size()){
        int sz = q.size();
        for(int i=0;i<sz;i++){
            auto node = q.front();
            q.pop();
            mn = min(mn,node.second);
            mx = max(mx,node.second);
            mp[node.second].push_back(node.first->val);
            if(node.first->left) q.push({node.first->left,node.second-1});
            if(node.first->right) q.push({node.first->right,node.second+1});
        }
    }
    vector<vector<int>> ans;
    for(int i=mn;i<=mx;i++)
        ans.emplace_back(mp[i]);
    return ans;
}