Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
p = [int(i) for i in input().split()]

class Unionfind:
    def __init__(self, num):
        self.par = [i for i in range(num+1)]
        self.rank = [0] * (num+1)

    def root(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.root(self.par[x])
            return self.par[x]

    def unite(self, u, v):
        ru = self.root(u)
        rv = self.root(v)
        if self.rank[ru] < self.rank[rv]:
            self.par[ru] = rv
        else:
            self.par[ry] = ru
            if self.rank[ru] == self.rank[rv]:
                self.rank[ru] += 1

    def same(self, u, v):
        return self.root(u) == self.root(v)

uni = Unionfind(N)
for i in range(M):
    x, y = map(int, input().split())
    uni.unite(x, y)

count = 0
for i in range(1, N+1):
    if uni.same(i, p[i-1]):
        count += 1

print(count)


Fixed submission:
N, M = map(int, input().split())
p = [int(i) for i in input().split()]

class Unionfind:
    def __init__(self, num):
        self.par = [i for i in range(num+1)]
        self.rank = [0] * (num+1)

    def root(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.root(self.par[x])
            return self.par[x]

    def unite(self, u, v):
        ru = self.root(u)
        rv = self.root(v)
        if self.rank[ru] < self.rank[rv]:
            self.par[ru] = rv
        else:
            self.par[rv] = ru
            if self.rank[ru] == self.rank[rv]:
                self.rank[ru] += 1

    def same(self, u, v):
        return self.root(u) == self.root(v)

uni = Unionfind(N)
for i in range(M):
    x, y = map(int, input().split())
    uni.unite(x, y)

count = 0
for i in range(1, N+1):
    if uni.same(i, p[i-1]):
        count += 1

print(count)

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
p = [int(i) for i in input().split()]

class Unionfind:
    def __init__(self, num):
        self.num = num
        self.par = [int(i) for i in range(num+1)]

    def root(self, x):
        if self.par[x] == x:
            return x
        else:
            return self.root(self.par[x])

    def unite(self, u, v):
        ru = self.root(u)
        rv = self.root(v)
        if ru != rv:
            self.par[ru] = rv

    def same(self, u, v):
        return self.root(u) == self.root(v)

uni = Unionfind(N)
for i in range(M):
    x, y = map(int, input().split())
    uni.unite(x, y)

count = 0
for i in range(1, N+1):
    if uni.same(i, p[i-1]):
        count += 1

print(count)


Fixed submission:
N, M = map(int, input().split())
p = [int(i) for i in input().split()]

class Unionfind:
    def __init__(self, num):
        self.par = [i for i in range(num+1)]
        self.rank = [0] * (num+1)

    def root(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.root(self.par[x])
            return self.par[x]

    def unite(self, u, v):
        ru = self.root(u)
        rv = self.root(v)
        if self.rank[ru] < self.rank[rv]:
            self.par[ru] = rv
        else:
            self.par[rv] = ru
            if self.rank[ru] == self.rank[rv]:
                self.rank[ru] += 1

    def same(self, u, v):
        return self.root(u) == self.root(v)

uni = Unionfind(N)
for i in range(M):
    x, y = map(int, input().split())
    uni.unite(x, y)

count = 0
for i in range(1, N+1):
    if uni.same(i, p[i-1]):
        count += 1

print(count)

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
p = [int(i) for i in input().split()]

class Unionfind:
    def __init__(self, num):
        self.num = num
        self.par = [int(i) for i in range(num+1)]

    def root(self, x):
        if self.par[x] == x:
            return x
        else:
            return self.root(self.par[x])

    def unite(self, u, v):
        ru = self.root(u)
        rv = self.root(v)
        if ru != rv:
            self.par[ru] = rv

    def same(self, u, v):
        return self.root(u) == self.root(v)

uni = Unionfind(N)
for i in range(M):
    x, y = map(int, input().split())
    uni.unite(x, y)

count = 0
for i in range(N, 0, -1):
    if uni.same(i, p[i-1]):
        count += 1

print(count)


Fixed submission:
N, M = map(int, input().split())
p = [int(i) for i in input().split()]

class Unionfind:
    def __init__(self, num):
        self.par = [i for i in range(num+1)]
        self.rank = [0] * (num+1)

    def root(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.root(self.par[x])
            return self.par[x]

    def unite(self, u, v):
        ru = self.root(u)
        rv = self.root(v)
        if self.rank[ru] < self.rank[rv]:
            self.par[ru] = rv
        else:
            self.par[rv] = ru
            if self.rank[ru] == self.rank[rv]:
                self.rank[ru] += 1

    def same(self, u, v):
        return self.root(u) == self.root(v)

uni = Unionfind(N)
for i in range(M):
    x, y = map(int, input().split())
    uni.unite(x, y)

count = 0
for i in range(1, N+1):
    if uni.same(i, p[i-1]):
        count += 1

print(count)