Vertical Order Traversal of a Binary Tree

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
 //BFS-Method
class Solution {
public:
    vector<vector<int>> verticalTraversal(TreeNode* root) {
        TreeNode *curr;
        queue<pair<TreeNode*, int>> q;
        q.push({root,0});
        vector<vector<int>> ans;
        map<int,vector<int>> mymap;
        
        //BFS
        while(!q.empty())
        {
            int size = q.size();            
            map<int,set<int>> mapset;
            
            while(size--)
            {
                curr = q.front().first;
                int col = q.front().second;
                q.pop();
                mapset[col].insert(curr->val);
                
                if(curr->left)
                    q.push({curr->left,col-1});
                if(curr->right)
                    q.push({curr->right,col+1});
            }
            for(auto it: mapset)
                for(auto it2: it.second)
                    mymap[it.first].push_back(it2);
        }
        //Now pass all values from mymap to ans array
        for(auto it: mymap)
            ans.push_back(it.second);
        
        return ans;
    }
};
//DFS Method
class Solution {
    map<int,map<int,set<int>>> mymap;
    void solve(TreeNode *curr,int col,int row)
    {
        if(!curr)
            return;
        
        mymap[col][row].insert(curr->val);
        solve(curr->left,col-1,row+1);
        solve(curr->right,col+1,row+1);
    }
public:
    vector<vector<int>> verticalTraversal(TreeNode* root) {
        solve(root,0,0);
        
        vector<vector<int>> ans;
        for(auto m1: mymap)
        {    
            ans.push_back(vector<int>());
            for(auto m2: m1.second)
            {
                for(auto m3: m2.second)
                    ans.back().push_back(m3);
            }
        }
        return ans;
    }
};

Use multiset instead of set