All Ancestors of a Node in a Directed Acyclic Graph LeetCode solution in Python

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# Runtime: 2132 ms (Top 14.62%) | Memory: 30.4 MB (Top 89.89%)
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class Solution:
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    def getAncestors(self, n: int, edges: List[List[int]]) -> List[List[int]]:
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        graph = {}
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        for a, b in edges:
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            graph[b] = graph.get(b, []) + [a]
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        op = [[] for i in range(n)]
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        for a in graph:
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            visited = set()
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            paths = [a]
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            while len(paths) > 0:
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                curr = paths.pop()
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                for b in graph.get(curr, []):
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                    if b not in visited:
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                        visited.add(b)
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                        paths.append(b)
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            op[a] = sorted(visited)
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        return op