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author | Vincent Ambo <mail@tazj.in> | 2021-12-13T22·51+0300 |
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committer | Vincent Ambo <mail@tazj.in> | 2021-12-13T23·15+0300 |
commit | 019f8fd2113df4c5247c3969c60fd4f0e08f91f7 (patch) | |
tree | 76a857f61aa88f62a30e854651e8439db77fd0ea /users/wpcarro/scratch/data_structures_and_algorithms/topo-sort.py | |
parent | 464bbcb15c09813172c79820bcf526bb10cf4208 (diff) | |
parent | 6123e976928ca3d8d93f0b2006b10b5f659eb74d (diff) |
subtree(users/wpcarro): docking briefcase at '24f5a642' r/3226
git-subtree-dir: users/wpcarro git-subtree-mainline: 464bbcb15c09813172c79820bcf526bb10cf4208 git-subtree-split: 24f5a642af3aa1627bbff977f0a101907a02c69f Change-Id: I6105b3762b79126b3488359c95978cadb3efa789
Diffstat (limited to 'users/wpcarro/scratch/data_structures_and_algorithms/topo-sort.py')
-rw-r--r-- | users/wpcarro/scratch/data_structures_and_algorithms/topo-sort.py | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/users/wpcarro/scratch/data_structures_and_algorithms/topo-sort.py b/users/wpcarro/scratch/data_structures_and_algorithms/topo-sort.py new file mode 100644 index 000000000000..fe295b0279ff --- /dev/null +++ b/users/wpcarro/scratch/data_structures_and_algorithms/topo-sort.py @@ -0,0 +1,31 @@ +from fixtures import unweighted_digraph +from collections import deque + +# vertices_no_in_edges :: UnweightedDigraph -> Set(Vertex) +def vertices_no_in_edges(g): + """Return the vertices in graph `g` with no in-edges.""" + result = set() + vertices = set(g.keys()) + for neighbors in g.values(): + result = result.union(neighbors) + return vertices ^ result + +# topo_sort :: UnweightedDigraph -> List(Vertex) +def topo_sort(g): + q = deque() + seen = set() + result = [] + for x in vertices_no_in_edges(g): + q.append(x) + while q: + vertex = q.popleft() + if vertex in seen: + continue + result.append(vertex) + neighbors = g.get(vertex) + for x in g.get(vertex): + q.append(x) + seen.add(vertex) + return result + +print(topo_sort(unweighted_digraph)) |