Adjacency List and Adjacency Matrix in Python

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Assuming:

edges = [('a', 'b'), ('a', 'b'), ('a', 'c')]

Here’s some code for the matrix:

from collections import defaultdict

matrix = defaultdict(int)
for edge in edges:
    matrix[edge] += 1

print matrix['a', 'b']

2

And for the “list”:

from collections import defaultdict

adj_list = defaultdict(lambda: defaultdict(lambda: 0))
for start, end in edges:
    adj_list[start][end] += 1

print adj_list['a']

{'c': 1, 'b': 2}

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