LeetCode/problems/0001-0499/323.py at main · nickleigh05/LeetCode · GitHub

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"""

323. Number of Connected Components in an Undirected Graph

Medium

You have a graph of n nodes. You are given an integer n and an array edges where edges[i] = [ai, bi] indicates that there is an edge between ai and bi in the graph.

Return the number of connected components in the graph.

Example 1:

    Input: n = 5, edges = [[0,1],[1,2],[3,4]]
    Output: 2

Example 2:

    Input: n = 5, edges = [[0,1],[1,2],[2,3],[3,4]]
    Output: 1

Constraints:

    1 <= n <= 2000
    1 <= edges.length <= 5000
    edges[i].length == 2
    0 <= ai <= bi < n
    ai != bi
    There are no repeated edges.

"""

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

        graph = [[] for _ in range(n)]
        for a, b in edges:
            graph[a].append(b)
            graph[b].append(a)

        visited = set()

        def dfs(node):
            for neighbor in graph[node]:
                if neighbor not in visited:
                    visited.add(neighbor)
                    dfs(neighbor)

        count = 0
        for i in range(n):
            if i not in visited:
                visited.add(i)
                dfs(i)
                count += 1

        return count