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# Kahn's Algorithm is used to find Topological ordering of Directed Acyclic Graph using BFS
def topologicalSort(l):
indegree = [0] * len(l)
queue = []
topo = []
cnt = 0
for key, values in l.items():
for i in values:
indegree[i] += 1
for i in range(len(indegree)):
if indegree[i] == 0:
queue.append(i)
while queue:
vertex = queue.pop(0)
cnt += 1
topo.append(vertex)
for x in l[vertex]:
indegree[x] -= 1
if indegree[x] == 0:
queue.append(x)
if cnt != len(l):
print("Cycle exists")
else:
print(topo)
# Adjacency List of Graph
l = {0: [1, 2], 1: [3], 2: [3], 3: [4, 5], 4: [], 5: []}
topologicalSort(l)