Trick: use a pair map

class Solution {
public:
    vector<vector<int>> verticalOrder(TreeNode* root) {
        if(!root) return {};
        vector<vector<int>> res;
        map<int, vector<int>> r;
        queue<pair<int, TreeNode*>> q;
        q.push(make_pair(0, root));
        while(!q.empty()){
            auto t = q.front(); q.pop();
            int f = t.first;
            TreeNode* tree = t.second;
            r[f].push_back(tree->val);
            if(tree->left) q.push(make_pair(f-1, tree->left));
            if(tree->right) q.push(make_pair(f+1, tree->right));
        }
        for(auto a:r){
            res.push_back(a.second);
        }
        return res;
    }
};