Problem p03108 (python)

Fixed submission:
import numpy as np


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 = list( map(int, input().split()) )

uf = UnionFind(N)
A = [0]*M
B = [0]*M
for i in range(M):
    a,b = list( map(int, input().split()) )
    A[i]=a-1
    B[i]=b-1

#print(A)
#print(B)

cmax = int(N*(N-1)/2)
FD = [cmax]*(M+1)
#print(FD)
for i in range(M):
    #print(uf)
    if uf.same(A[M-i-1],B[M-i-1]):
        FD[M-i-1] = FD[M-i]
    else:
        cless = uf.size(A[M-i-1])*uf.size(B[M-i-1])
        FD[M-i-1] = FD[M-i] - cless
        if FD[M-i-1]<0: FD[M-i-1]=0
    uf.union(A[M-1-i],B[M-1-i])

#print(uf)
#print(FD[1:])
for fd in FD[1:]:
    print(fd)

Buggy submission (verdict: Runtime Error):
import numpy as np


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 = list( map(int, input().split()) )

uf = UnionFind(N)
A = [0]*M
B = [0]*M
for i in range(M):
    a,b = list( map(int, input().split()) )
    A[i]=a-1
    B[i]=b-1

#print(A)
#print(B)

cmax = int(N*(N-1)/2)
FD = [cmax]*(M+1)
#print(FD)
for i in range(M):
    #print(uf)
    if uf.same(A[M-i-1],B[M-i-1]):
        FD[M-i-1] = FD[M-i]
    else:
        cless = uf.size(A[M-i-1])*uf.size(B[M-i-1])
        FD[M-i-1] = FD[M-i] - cless
        if FD[M-i-1]<0: FD[M-i-1]=0
    uf.union(A[M-1-i],B[M-1-i])

#print(uf)
#print(FD[1:])
for fd in FD[1:]:
    print(fd)

Buggy submission (verdict: Runtime Error):
#import numpy as np


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 = list( map(int, input().split()) )

uf = UnionFind(N)
A = [0]*M
B = [0]*M
for i in range(M):
    a,b = list( map(int, input().split()) )
    A[i]=a-1
    B[i]=b-1

#print(A)
#print(B)

cmax = int(N*(N-1)/2)
FD = [cmax]*(M+1)
#print(FD)
for i in range(M):
    #print(uf)
    if same(A[M-i-1])*uf.size(B[M-i-1]):
        FD[M-i-1] = FD[M-i]
    else:
        cless = uf.size(A[M-i-1])*uf.size(B[M-i-1])
        FD[M-i-1] = FD[M-i] - cless
        if FD[M-i-1]<0: FD[M-i-1]=0
    uf.union(A[M-1-i],B[M-1-i])

#print(uf)
#print(FD[1:])
for fd in FD[1:]:
    print(fd)