Python/graphs/bellman_ford.py

55 lines
1.3 KiB
Python
Raw Normal View History

2018-10-19 12:48:28 +00:00
from __future__ import print_function
def printDist(dist, V):
print("\nVertex Distance")
for i in range(V):
if dist[i] != float('inf') :
print(i,"\t",int(dist[i]),end = "\t")
else:
print(i,"\t","INF",end="\t")
print()
def BellmanFord(graph, V, E, src):
mdist=[float('inf') for i in range(V)]
mdist[src] = 0.0
2018-10-19 12:48:28 +00:00
for i in range(V-1):
for j in range(V):
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
2018-10-19 12:48:28 +00:00
for j in range(V):
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)
if __name__ == "__main__":
V = int(input("Enter number of vertices: ").strip())
E = int(input("Enter number of edges: ").strip())
2018-10-19 12:48:28 +00:00
graph = [dict() for j in range(E)]
2018-10-19 12:48:28 +00:00
for i in range(V):
graph[i][i] = 0.0
2018-10-19 12:48:28 +00:00
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}
2018-10-19 12:48:28 +00:00
gsrc = int(input("\nEnter shortest path source:").strip())
BellmanFord(graph, V, E, gsrc)