Critical Connections in a Network LeetCode solution in Python

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class Solution:
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    def criticalConnections(
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        self, n: int, connections: List[List[int]]
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    ) -> List[List[int]]:
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        dic = collections.defaultdict(list)
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        for c in connections:
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            u, v = c
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            dic[u].append(v)
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            dic[v].append(u)
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        timer = 0
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        depth, lowest, parent, visited = (
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            [float("inf")] * n,
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            [float("inf")] * n,
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            [float("inf")] * n,
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            [False] * n,
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        )
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        res = []
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        def find(u):
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            nonlocal timer
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            visited[u] = True
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            depth[u], lowest[u] = timer, timer
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            timer += 1
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            for v in dic[u]:
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                if not visited[v]:
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                    parent[v] = u
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                    find(v)
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                    if lowest[v] > depth[u]:
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                        res.append([u, v])
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                if parent[u] != v:
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                    lowest[u] = min(lowest[u], lowest[v])
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        find(0)
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        return res