Solution.py

class Solution:
    def findSmallestRegion(
        self, regions: List[List[str]], region1: str, region2: str
    ) -> str:
        m = {}
        for region in regions:
            for r in region[1:]:
                m[r] = region[0]
        s = set()
        while m.get(region1):
            s.add(region1)
            region1 = m[region1]
        while m.get(region2):
            if region2 in s:
                return region2
            region2 = m[region2]
        return region1