Vertical Traversal - 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) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> verticalTraversal(TreeNode* root) {
        if(root==nullptr)   return {};
        unordered_map<int, vector<int>> xToVector;

        queue<pair<TreeNode*, int>> q;
        q.push({root, 0});
        int leftBoundary = INT_MAX; int rightBoundary = INT_MIN;

        pair<TreeNode*, int> temp;

        unordered_map<int, set<int>> formedSoFar;
        int l_leftBoundary = INT_MAX, l_rightBoundary = INT_MIN;

        while(!q.empty()){
            int qSize = q.size();
            while(qSize--){
                //all these temp's have same y coordinate
                temp = q.front(); q.pop();


                l_leftBoundary = min(l_leftBoundary, temp.second);
                l_rightBoundary = max(l_rightBoundary, temp.second);

                if((temp.first)->left != nullptr){
                    q.push({(temp.first)->left, temp.second-1});
                }
                if((temp.first)->right != nullptr){
                    q.push({(temp.first)->right, temp.second+1});
                }
                formedSoFar[temp.second].insert((temp.first)->val);

            }
            leftBoundary = min(leftBoundary, l_leftBoundary);
            rightBoundary = max(rightBoundary, l_rightBoundary);

            for(int i=l_leftBoundary; i<=l_rightBoundary; i++){
                for(auto &vl: formedSoFar[i]){
                    xToVector[i].push_back(vl);
                }
            }

            formedSoFar.clear();
        }
        //cout << leftBoundary << " " << rightBoundary << endl;
        vector<vector<int>> answer;

        for(int i=leftBoundary; i<=rightBoundary; i++){
            if(xToVector.count(i)){
                answer.push_back(xToVector[i]);
            }
        }

        return answer;

    }
};