Buggy python submission (verdict: Runtime Error):
N, M = [int(_) for _ in input().split()]
AB = [[int(_) for _ in input().split()] for _ in range(M)]

UF = list(range(N + 1))
SIZE = [0] + [1] * N  # 1-indexed


def find(x):
    if UF[x] != x:
        UF[x] = find(UF[x])
    return UF[x]


def unite(x, y):
    if not is_same(x, y):
        X, Y = find(x), find(y)
        SX, SY = SIZE[X], SIZE[Y]
        if SX > SY:
            m = UF[X] = Y
        else:
            m = UF[Y] = X
        SIZE[m] = SX + SY
        SIZE[X + Y - m] = 0


def is_same(x, y):
    return find(x) == find(y)


def scan_uf():
    for i in range(len(UF)):
        find(i)


ans = [N * (N - 1) // 2]
for a, b in AB[::-1]:
    if not is_same(a, b):
        ans += [ans[-1] - SIZE[find(a)] * SIZE[find(b)]]
        unite(a, b)
    else:
        ans += [ans[-1]]
print(*ans[M - 1::-1], sep='\n')


Fixed submission:
N, M = [int(_) for _ in input().split()]
AB = [[int(_) for _ in input().split()] for _ in range(M)]

UF = list(range(N + 1))
SIZE = [1] * (N + 1)


def find(x):
    if UF[x] != x:
        UF[x] = find(UF[x])
    return UF[x]


def unite(x, y):
    m = min(find(x), find(y))
    SIZE[m] = SIZE[find(x)] + SIZE[find(y)]
    UF[find(x)] = m
    UF[find(y)] = m


def is_same(x, y):
    return find(x) == find(y)


ans = [N * (N - 1) // 2]
for a, b in AB[::-1]:
    if not is_same(a, b):
        ans += [ans[-1] - SIZE[find(a)] * SIZE[find(b)]]
        unite(a, b)
    else:
        ans += [ans[-1]]
print(*ans[M - 1::-1], sep='\n')

Buggy python submission (verdict: Runtime Error):
N, M = [int(_) for _ in input().split()]
AB = [[int(_) for _ in input().split()] for _ in range(M)]

UF = list(range(N + 1))
SIZE = [0] + [1] * N  # 1-indexed


def find(x):
    if UF[x] != x:
        UF[x] = find(UF[x])
    return UF[x]


def unite(x, y):
    if not is_same(x, y):
        X, Y = find(x), find(y)
        SX, SY = SIZE[X], SIZE[Y]
        if SX > SY:
            m = UF[X] = Y
        else:
            m = UF[Y] = X
        SIZE[m] = SX + SY
        SIZE[X + Y - m] = 0


def is_same(x, y):
    return find(x) == find(y)


def scan_uf():
    for i in range(len(UF)):
        find(i)


ans = [N * (N - 1) // 2]
for a, b in AB[::-1]:
    if not is_same(a, b):
        ans += [ans[-1] - SIZE[find(a)] * SIZE[find(b)]]
        unite(a, b)
    else:
        ans += [ans[-1]]
print(*ans[-2::-1], sep='\n')


Fixed submission:
N, M = [int(_) for _ in input().split()]
AB = [[int(_) for _ in input().split()] for _ in range(M)]

UF = list(range(N + 1))
SIZE = [1] * (N + 1)


def find(x):
    if UF[x] != x:
        UF[x] = find(UF[x])
    return UF[x]


def unite(x, y):
    m = min(find(x), find(y))
    SIZE[m] = SIZE[find(x)] + SIZE[find(y)]
    UF[find(x)] = m
    UF[find(y)] = m


def is_same(x, y):
    return find(x) == find(y)


ans = [N * (N - 1) // 2]
for a, b in AB[::-1]:
    if not is_same(a, b):
        ans += [ans[-1] - SIZE[find(a)] * SIZE[find(b)]]
        unite(a, b)
    else:
        ans += [ans[-1]]
print(*ans[M - 1::-1], sep='\n')

Buggy python submission (verdict: Runtime Error):
N, M = [int(_) for _ in input().split()]
AB = [[int(_) for _ in input().split()] for _ in range(M)]

UF = list(range(N + 1))
SIZE = [0] + [1] * N  # 1-indexed


def find(x):
    if UF[x] != x:
        UF[x] = find(UF[x])
    return UF[x]


def unite(x, y):
    if not is_same(x, y):
        X, Y = find(x), find(y)
        SX, SY = SIZE[X], SIZE[Y]
        if SX > SY:
            m = UF[X] = Y
        else:
            m = UF[Y] = X
        SIZE[m] = SX + SY
        SIZE[X + Y - m] = 0


def is_same(x, y):
    return find(x) == find(y)


def scan_uf():
    for i in range(len(UF)):
        find(i)


ans = [N * (N - 1) // 2]
for a, b in AB[::-1]:
    sA = SIZE[find(a)]
    sB = SIZE[find(b)]
    unite(a, b)
    new = SIZE[find(a)]
    ans += [
        ans[-1] - new * (new - 1) // 2 + sA * (sA - 1) // 2 +
        sB * (sB - 1) // 2
    ]
print(*ans[-2::-1], sep='\n')


Fixed submission:
N, M = [int(_) for _ in input().split()]
AB = [[int(_) for _ in input().split()] for _ in range(M)]

UF = list(range(N + 1))
SIZE = [1] * (N + 1)


def find(x):
    if UF[x] != x:
        UF[x] = find(UF[x])
    return UF[x]


def unite(x, y):
    m = min(find(x), find(y))
    SIZE[m] = SIZE[find(x)] + SIZE[find(y)]
    UF[find(x)] = m
    UF[find(y)] = m


def is_same(x, y):
    return find(x) == find(y)


ans = [N * (N - 1) // 2]
for a, b in AB[::-1]:
    if not is_same(a, b):
        ans += [ans[-1] - SIZE[find(a)] * SIZE[find(b)]]
        unite(a, b)
    else:
        ans += [ans[-1]]
print(*ans[M - 1::-1], sep='\n')