Bottom view of binary tree

from collections import defaultdict
class Solution:
    def bottomView(self, root):
        q=deque()
        q.append((root,0))
        d=defaultdict(list)
        while q:
            for _ in range(len(q)):
                t,v=q.popleft()
                d[v].append(t.data)
                if t.left:q.append((t.left,v-1))
                if t.right:q.append((t.right,v+1))
        ans=[]
        for i in sorted(d.keys()):
            ans.append(d[i][-1])
        return ans