Number of connected components in a graph

class Solution:
    def countComponents(self, n: int, edges: List[List[int]]) -> int:


        def dfs(node: int) -> None:
            if node in visited:
                return

            visited.add(node)

            for nb in hashmap[node]:
                dfs(nb)


        hashmap = defaultdict(list)
        for e in edges:
            a, b = e
            hashmap[a].append(b)
            hashmap[b].append(a)

        visited = set()
        count = 0

        for i in range(n):
            if i not in visited:
                dfs(i)
                count += 1

        return count