Python/graphs/bellman_ford.py
Christian Clauss 9200a2e543
from __future__ import annotations (#2464)
* from __future__ import annotations

* fixup! from __future__ import annotations

* fixup! from __future__ import annotations

* fixup! Format Python code with psf/black push

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
2020-09-23 13:30:13 +02:00

57 lines
1.6 KiB
Python

from __future__ import annotations
def printDist(dist, V):
print("Vertex Distance")
distances = ("INF" if d == float("inf") else d for d in dist)
print("\t".join(f"{i}\t{d}" for i, d in enumerate(distances)))
def BellmanFord(graph: list[dict[str, int]], V: int, E: int, src: int) -> int:
"""
Returns shortest paths from a vertex src to all
other vertices.
"""
mdist = [float("inf") for i in range(V)]
mdist[src] = 0.0
for i in range(V - 1):
for j in range(E):
u = graph[j]["src"]
v = graph[j]["dst"]
w = graph[j]["weight"]
if mdist[u] != float("inf") and mdist[u] + w < mdist[v]:
mdist[v] = mdist[u] + w
for j in range(E):
u = graph[j]["src"]
v = graph[j]["dst"]
w = graph[j]["weight"]
if mdist[u] != float("inf") and mdist[u] + w < mdist[v]:
print("Negative cycle found. Solution not possible.")
return
printDist(mdist, V)
return src
if __name__ == "__main__":
V = int(input("Enter number of vertices: ").strip())
E = int(input("Enter number of edges: ").strip())
graph = [dict() for j in range(E)]
for i in range(E):
graph[i][i] = 0.0
for i in range(E):
print("\nEdge ", i + 1)
src = int(input("Enter source:").strip())
dst = int(input("Enter destination:").strip())
weight = float(input("Enter weight:").strip())
graph[i] = {"src": src, "dst": dst, "weight": weight}
gsrc = int(input("\nEnter shortest path source:").strip())
BellmanFord(graph, V, E, gsrc)