并查集连了两次之后

五个点各自一块。先 union(0, 2)，再 union(3, 4)。运行下面这段程序，看三件事：0 和 2 连通了吗、0 和 3 连通了吗、现在还剩几块：

def make(verts):
    return {u: u for u in verts}

def find(p, x):
    while p[x] != x:
        p[x] = p[p[x]]
        x = p[x]
    return x

def union(p, a, b):
    ra, rb = find(p, a), find(p, b)
    if ra == rb:
        return False
    p[ra] = rb
    return True

p = make([0, 1, 2, 3, 4])
union(p, 0, 2)
union(p, 3, 4)
print(str(find(p, 0) == find(p, 2)) + "/" + str(find(p, 0) == find(p, 3)) + "/" + str(len({find(p, u) for u in [0, 1, 2, 3, 4]})))