mathdatech/Python
1
0
Fork 0
mirror of https://github.com/TheAlgorithms/Python.git synced 2025-04-29 09:03:36 +00:00
Code Issues Packages Projects Releases Wiki Activity

[pre-commit.ci] auto fixes from pre-commit.com hooks

Browse Source 
for more information, see https://pre-commit.ci
This commit is contained in:
pre-commit-ci[bot] 2024-10-10 22:56:49 +00:00
parent f8a94a8b00
commit 0154a8a56a
1 changed files with 23 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
graphs/bellman_ford.py
View File

@ -17,20 +17,29 @@ def print_distance_and_paths(distance: list[float], paths: list[list[int]], src:
print(f"{vertex}\t\t{dist}\t\t\t\t{path_str}")
def check_negative_cycle(graph: list[Edge], distance: list[float], predecessor: list[int]) -> bool:
def check_negative_cycle(
graph: list[Edge], distance: list[float], predecessor: list[int]
) -> bool:
"""
Checks if there is a negative weight cycle reachable from the source vertex.
If found, return True, indicating a negative cycle.
"""
for edge in graph:
if distance[edge.src] != float("inf") and distance[edge.src] + edge.weight < distance[edge.dst]:
if (
distance[edge.src] != float("inf")
and distance[edge.src] + edge.weight < distance[edge.dst]
):
# Update predecessors to indicate a cycle for affected paths
predecessor[edge.dst] = -1 # Use -1 as a marker for negative cycle detection
predecessor[
edge.dst
] = -1 # Use -1 as a marker for negative cycle detection
return True
return False
def reconstruct_paths(predecessor: list[int], vertex_count: int, src: int) -> list[list[int]]:
def reconstruct_paths(
predecessor: list[int], vertex_count: int, src: int
) -> list[list[int]]:
"""
Reconstructs the shortest paths from the source vertex to each vertex using the predecessor list.
"""
@ -50,7 +59,9 @@ def reconstruct_paths(predecessor: list[int], vertex_count: int, src: int) -> li
return paths
def bellman_ford(graph: list[Edge], vertex_count: int, src: int) -> tuple[list[float], list[list[int]]]:
def bellman_ford(
graph: list[Edge], vertex_count: int, src: int
) -> tuple[list[float], list[list[int]]]:
"""
Returns the shortest paths from a vertex src to all other vertices, including path reconstruction.
"""
@ -61,7 +72,10 @@ def bellman_ford(graph: list[Edge], vertex_count: int, src: int) -> tuple[list[f
# Step 1: Relax edges repeatedly
for _ in range(vertex_count - 1):
for edge in graph:
if distance[edge.src] != float("inf") and distance[edge.src] + edge.weight < distance[edge.dst]:
if (
distance[edge.src] != float("inf")
and distance[edge.src] + edge.weight < distance[edge.dst]
):
distance[edge.dst] = distance[edge.src] + edge.weight
predecessor[edge.dst] = edge.src
@ -88,7 +102,9 @@ if __name__ == "__main__":
for i in range(E):
print(f"Edge {i + 1}")
src, dest, weight = map(int, input("Enter source, destination, weight: ").strip().split())
src, dest, weight = map(
int, input("Enter source, destination, weight: ").strip().split()
)
if src < 0 or src >= V or dest < 0 or dest >= V:
print(f"Invalid vertices: src and dest should be between 0 and {V - 1}")
continue