Python/graphs/minimum_spanning_tree_kruskal.py
Christian Clauss cecf43d648
Pyupgrade to Python 3.9 (#4718)
* Pyupgrade to Python 3.9

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
2021-09-07 13:37:03 +02:00

47 lines
1.3 KiB
Python

def kruskal(
num_nodes: int, edges: list[tuple[int, int, int]]
) -> list[tuple[int, int, int]]:
"""
>>> kruskal(4, [(0, 1, 3), (1, 2, 5), (2, 3, 1)])
[(2, 3, 1), (0, 1, 3), (1, 2, 5)]
>>> kruskal(4, [(0, 1, 3), (1, 2, 5), (2, 3, 1), (0, 2, 1), (0, 3, 2)])
[(2, 3, 1), (0, 2, 1), (0, 1, 3)]
>>> kruskal(4, [(0, 1, 3), (1, 2, 5), (2, 3, 1), (0, 2, 1), (0, 3, 2),
... (2, 1, 1)])
[(2, 3, 1), (0, 2, 1), (2, 1, 1)]
"""
edges = sorted(edges, key=lambda edge: edge[2])
parent = list(range(num_nodes))
def find_parent(i):
if i != parent[i]:
parent[i] = find_parent(parent[i])
return parent[i]
minimum_spanning_tree_cost = 0
minimum_spanning_tree = []
for edge in edges:
parent_a = find_parent(edge[0])
parent_b = find_parent(edge[1])
if parent_a != parent_b:
minimum_spanning_tree_cost += edge[2]
minimum_spanning_tree.append(edge)
parent[parent_a] = parent_b
return minimum_spanning_tree
if __name__ == "__main__": # pragma: no cover
num_nodes, num_edges = list(map(int, input().strip().split()))
edges = []
for _ in range(num_edges):
node1, node2, cost = (int(x) for x in input().strip().split())
edges.append((node1, node2, cost))
kruskal(num_nodes, edges)