def count_users(group):
    count = 0
    for member in get_members(group):
    #count += 1
        if is_group(member):
            count += count_users(member)
        else:
            count+=1
    return count

print(count_users("sales")) # Should be 3
print(count_users("engineering")) # Should be 8
print(count_users("everyone")) # Should be 18

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问题出在for循环中。目前，对于组中的每个“成员”，计数增加1，即使该成员本身就是一个组。相反，将该行移动到if is_group（member）之后的一个新的else分支中，因此如果member是一个组，则只增加成员数，如果member不是一个组，则只增加1。

def count_users(group):
  count = 0
  for member in get_members(group):
    count += 1
    if is_group(member):
      count += count_users(member)-1
  return count

print(count_users("sales")) # Should be 3
print(count_users("engineering")) # Should be 8
print(count_users("everyone")) # Should be 18

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下面是正确的解决方案：

def count_users(group):
  count = 0
  for member in get_members(group):
    count += 1
    if is_group(member):
      count += count_users(member)-1
 return count

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print(count_users("sales")) #应该是3
print(count_users("engineering")) #应该是8
print(count_users("everyone")) #应该是18

def count_users(group):
  count = 0
  for member in get_members(group):
    count += 1
    if is_group(member):
      count += count_users(member)
      count -= 1
  return count

print(count_users("sales")) # Should be 3
print(count_users("engineering")) # Should be 8
print(count_users("everyone")) # Should be 18

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count -= 1意味着一个假设的成员，结果是一个组，只需要从count变量中删除。

def count_users(group):
  count = 0
  for member in get_members(group):
    #count += 1
    if is_group(member):
      count += count_users(member)
    else:
      count += 1
  return count

print(count_users("sales")) # Should be 3
print(count_users("engineering")) # Should be 8
print(count_users("everyone")) # Should be 18

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