Find the City With the Smallest Number of Neighbors at a Threshold Distance LeetCode solution in Python

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class Solution:
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    def findTheCity(
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        self, n: int, edges: List[List[int]], distanceThreshold: int
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    ) -> int:
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        matrix = [[float("inf")] * n for _ in range(n)]
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        # initializing the matrix
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        for u, v, w in edges:
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            matrix[u][v] = w
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            matrix[v][u] = w
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        for u in range(n):
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            matrix[u][u] = 0
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        for k in range(n):
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            for i in range(n):
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                for j in range(n):
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                    if matrix[i][j] > matrix[i][k] + matrix[k][j]:
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                        matrix[i][j] = matrix[i][k] + matrix[k][j]
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        # counting reachable cities(neighbor) for every single city
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        res = [0] * n
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        for i in range(len(matrix)):
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            for j in range(len(matrix[0])):
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                if 0 < matrix[i][j] <= distanceThreshold:
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                    res[j] += 1
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        return [i for i, x in enumerate(res) if x == min(res)][-1]