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class dsu(): | |
n=1 | |
parent_or_size=[-1 for i in range(n)] | |
def __init__(self,N): | |
self.n=N | |
self.parent_or_size=[-1 for i in range(N)] | |
def merge(self,a,b): | |
assert 0<=a<self.n, "0<=a<n,a={0},n={1}".format(a,self.n) | |
assert 0<=b<self.n, "0<=b<n,b={0},n={1}".format(b,self.n) | |
x=self.leader(a) | |
y=self.leader(b) | |
if x==y: | |
return x | |
if (-self.parent_or_size[x]<-self.parent_or_size[y]): | |
x,y=y,x | |
self.parent_or_size[x]+=self.parent_or_size[y] | |
self.parent_or_size[y]=x | |
return x | |
def same(self,a,b): | |
assert 0<=a<self.n, "0<=a<n,a={0},n={1}".format(a,self.n) | |
assert 0<=b<self.n, "0<=b<n,b={0},n={1}".format(b,self.n) | |
return self.leader(a)==self.leader(b) | |
def leader(self,a): | |
assert 0<=a<self.n, "0<=a<n,a={0},n={1}".format(a,self.n) | |
if (self.parent_or_size[a]<0): | |
return a | |
self.parent_or_size[a]=self.leader(self.parent_or_size[a]) | |
return self.parent_or_size[a] | |
def size(self,a): | |
assert 0<=a<self.n, "0<=a<n,a={0},n={1}".format(a,self.n) | |
return -self.parent_or_size[self.leader(a)] | |
def groups(self): | |
leader_buf=[0 for i in range(self.n)] | |
group_size=[0 for i in range(self.n)] | |
for i in range(self.n): | |
leader_buf[i]=self.leader(i) | |
group_size[leader_buf[i]]+=1 | |
result=[[] for i in range(self.n)] | |
for i in range(self.n): | |
result[leader_buf[i]].append(i) | |
result2=[] | |
for i in range(self.n): | |
if len(result[i])>0: | |
result2.append(result[i]) | |
return result2 | |
N=int(input()) | |
a=[int(i) for i in input().split()] | |
G=dsu(N) | |
for i in range(N): | |
G.merge(i,a[i]) | |
print(N-len(G.groups())) |
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