987-Vertical_Order_Traversal_of_a_Binary_Tree.cpp

class Solution {
public:
    
    
    vector<vector<int>> verticalTraversal(TreeNode* root) {
 

   // map will store {vertical,{level, multiple same value of nodes data}}
   // {0,{0,1}} {0,{2,{10,9}}} {0,{4,6}}
    map<int, map<int, multiset<int>>> nodes;
        
   //in a queue {root,{0,0}} --> {node,{vertical,level}}
    queue<pair<TreeNode *, pair<int, int>>> todo;
        
    todo.push({root,{0,0}}); // initial vertical and level


    while (!todo.empty())
    {
        auto p = todo.front();
        todo.pop();
        TreeNode *temp = p.first;

        // x -> vertical , y->level
        int x = p.second.first, y = p.second.second;
        // inserting like nodes[vertical ka value][level ka value] = {node ka data(it can be multiple)}
        
        nodes[x][y].insert(temp->val); // inserting to multiset

        if (temp->left)
        {
            todo.push({temp->left,{x - 1,y + 1}});
        }
        if (temp->right)
        {
            todo.push({temp->right,{x + 1,y + 1}});
        }
    }

 

    vector<vector<int>> ans;
    for (auto p : nodes)
    {
        vector<int> col;
        for (auto q : p.second)
        {
            col.insert(col.end(), q.second.begin(), q.second.end());
        }
        ans.push_back(col);
    }

    return ans;
}

};