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* ci(pre-commit): Add ``flake8-builtins`` additional dependency to ``pre-commit`` (#7104) * refactor: Fix ``flake8-builtins`` (#7104) * fix(lru_cache): Fix naming conventions in docstrings (#7104) * ci(pre-commit): Order additional dependencies alphabetically (#7104) * fix(lfu_cache): Correct function name in docstring (#7104) * Update strings/snake_case_to_camel_pascal_case.py Co-authored-by: Christian Clauss <cclauss@me.com> * Update data_structures/stacks/next_greater_element.py Co-authored-by: Christian Clauss <cclauss@me.com> * Update digital_image_processing/index_calculation.py Co-authored-by: Christian Clauss <cclauss@me.com> * Update graphs/prim.py Co-authored-by: Christian Clauss <cclauss@me.com> * Update hashes/djb2.py Co-authored-by: Christian Clauss <cclauss@me.com> * refactor: Rename `_builtin` to `builtin_` ( #7104) * fix: Rename all instances (#7104) * refactor: Update variable names (#7104) * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * ci: Create ``tox.ini`` and ignore ``A003`` (#7123) * revert: Remove function name changes (#7104) * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Rename tox.ini to .flake8 * Update data_structures/heap/heap.py Co-authored-by: Dhruv Manilawala <dhruvmanila@gmail.com> * refactor: Rename `next_` to `next_item` (#7104) * ci(pre-commit): Add `flake8` plugin `flake8-bugbear` (#7127) * refactor: Follow `flake8-bugbear` plugin (#7127) * fix: Correct `knapsack` code (#7127) * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci Co-authored-by: Christian Clauss <cclauss@me.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> Co-authored-by: Dhruv Manilawala <dhruvmanila@gmail.com>
74 lines
2.3 KiB
Python
74 lines
2.3 KiB
Python
from __future__ import annotations
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def print_distance(distance: list[float], src):
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print(f"Vertex\tShortest Distance from vertex {src}")
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for i, d in enumerate(distance):
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print(f"{i}\t\t{d}")
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def check_negative_cycle(
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graph: list[dict[str, int]], distance: list[float], edge_count: int
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):
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for j in range(edge_count):
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u, v, w = (graph[j][k] for k in ["src", "dst", "weight"])
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if distance[u] != float("inf") and distance[u] + w < distance[v]:
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return True
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return False
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def bellman_ford(
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graph: list[dict[str, int]], vertex_count: int, edge_count: int, src: int
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) -> list[float]:
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"""
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Returns shortest paths from a vertex src to all
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other vertices.
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>>> edges = [(2, 1, -10), (3, 2, 3), (0, 3, 5), (0, 1, 4)]
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>>> g = [{"src": s, "dst": d, "weight": w} for s, d, w in edges]
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>>> bellman_ford(g, 4, 4, 0)
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[0.0, -2.0, 8.0, 5.0]
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>>> g = [{"src": s, "dst": d, "weight": w} for s, d, w in edges + [(1, 3, 5)]]
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>>> bellman_ford(g, 4, 5, 0)
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Traceback (most recent call last):
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...
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Exception: Negative cycle found
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"""
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distance = [float("inf")] * vertex_count
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distance[src] = 0.0
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for _ in range(vertex_count - 1):
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for j in range(edge_count):
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u, v, w = (graph[j][k] for k in ["src", "dst", "weight"])
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if distance[u] != float("inf") and distance[u] + w < distance[v]:
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distance[v] = distance[u] + w
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negative_cycle_exists = check_negative_cycle(graph, distance, edge_count)
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if negative_cycle_exists:
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raise Exception("Negative cycle found")
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return distance
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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V = int(input("Enter number of vertices: ").strip())
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E = int(input("Enter number of edges: ").strip())
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graph: list[dict[str, int]] = [dict() for j in range(E)]
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for i in range(E):
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print("Edge ", i + 1)
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src, dest, weight = (
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int(x)
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for x in input("Enter source, destination, weight: ").strip().split(" ")
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)
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graph[i] = {"src": src, "dst": dest, "weight": weight}
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source = int(input("\nEnter shortest path source:").strip())
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shortest_distance = bellman_ford(graph, V, E, source)
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print_distance(shortest_distance, 0)
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