Vertical Traversal - Tree

from collections import defaultdict
from collections import deque

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def verticalOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        result = []
        if root is None:
            return result
        
        map = defaultdict(list)
        q = deque()
        index = deque()

        mini = 0
        q.append(root)
        index.append(0)
        
        while(q):
            curr = q.popleft()
            idx = index.popleft()
            
            map[idx].append(curr.val)
            
            if curr.left :
                q.append(curr.left)
                index.append(idx - 1)
            
            if curr.right :
                q.append(curr.right)
                index.append(idx + 1)
                
            mini = min(mini, idx)
            
        while(map[mini]):
            result.append(map.get(mini))
            mini += 1
        
        return result