Problem p03354 (python)

Fixed submission:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

N, M = map(int,input().split())
P = list(map(int,input().split()))
uf = UnionFind(N+1)
for i in range(M):
    a, b = map(int,input().split())
    uf.union(a,b)
ans = 0
for i in range(1,N+1):
    if uf.same(i,P[i-1]):
        ans += 1
print(ans)

Buggy submission (verdict: Runtime Error):
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

N, M = map(int,input().split())
P = list(map(int,input().split()))
uf = UnionFind(N)
for i in range(N):
    x, y = map(int,input().split())
    uf.union(x,y)
A = list(uf.all_group_members().values())
a = len(A)
B =[[] for i in range(a)]
import bisect
for i in range(a):
    S = A[i]
    for j in range(len(S)):
        insert_index = bisect.bisect_left(B[i],S[j])
        B[i].insert(insert_index,S[j])
    p = 0
    ans = 0
    for k in range(len(S)):
        if p == 0:
            x = B[i].pop
            p = 1
        if x == S[k]:
            p = 0
    ans += len(S) - len(B[i]) + p
print(ans)