Vertical Order Traversal of a Binary Tree

 

  Vertical Order Traversal of a Binary Tree

Given a binary tree, return the vertical order traversal of its nodes values.

For each node at position (X, Y), its left and right children respectively will be at positions (X-1, Y-1) and (X+1, Y-1).

Running a vertical line from X = -infinity to X = +infinity, whenever the vertical line touches some nodes, we report the values of the nodes in order from top to bottom (decreasing Y coordinates).

If two nodes have the same position, then the value of the node that is reported first is the value that is smaller.

Return an list of non-empty reports in order of X coordinate. Every report will have a list of values of nodes.

 

 /**
 * 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==NULL)
    {
        return {};
    }
    map<int,vector<int>>m;
    vector<vector<int>>v;
   
    queue<pair<TreeNode*,int>>q;
    q.push({root,1});
    
    while(!q.empty())
    {
        int k=q.size();
        map<int,set<int>>m1;
        
    while(k--)
    {
        TreeNode*curr=q.front().first;
        int hd=q.front().second;
        q.pop();
        m1[hd].insert(curr->val);
        if(curr->left)
        {
            q.push({curr->left,hd-1});
        }
        if(curr->right)
        {
            q.push({curr->right,hd+1});
        }
    }
    for(auto x:m1)
    {
        for(auto d:x.second)
        {
        m[x.first].push_back(d);
        }
    }
        
    }
    for(auto x:m)
    {
        v.push_back(x.second);
    }
    return v;
    }
};