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# Uses python3
import sys
sys.setrecursionlimit(200000)
def explore(v, adj, visited, postV, clock):
visited[v] = True
for w in adj[v]:
if visited[w] == False:
explore(w, adj, visited, postV, clock)
postV[v] = clock[0]
clock[0] = clock[0] + 1
def reverseG(adj):
adjReverse = [[] for _ in range(len(adj))]
for v in range(len(adj)):
for w in adj[v]:
adjReverse[w].append(v)
return adjReverse
def dfs(adj, visited, postV, clock):
for v in range(len(adj)):
if visited[v] == False:
explore(v, adj, visited, postV, clock)
def exploreWithoutPostV(v, adj, visited):
visited[v] = True
for w in adj[v]:
if visited[w] == False:
exploreWithoutPostV(w, adj, visited)
def number_of_strongly_connected_components(adj):
adjReversal = reverseG(adj)
adjReversalVisited = [False] * len(adj)
postV = [0] * len(adj)
clock = [0]
dfs(adjReversal, adjReversalVisited, postV, clock)
temp = sorted(range(len(postV)), key=lambda k: postV[k], reverse=True)
visited = [False] * len(adj)
result = 0
for i in temp:
if visited[i] == False:
exploreWithoutPostV(i, adj, visited)
result = result + 1
return result
if __name__ == '__main__':
input = sys.stdin.read()
data = list(map(int, input.split()))
n, m = data[0:2]
data = data[2:]
edges = list(zip(data[0:(2 * m):2], data[1:(2 * m):2]))
adj = [[] for _ in range(n)]
for (a, b) in edges:
adj[a - 1].append(b - 1)
print(number_of_strongly_connected_components(adj))
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