如何检查一个元素是否在集合中?
是否有与以下代码更简单的等效代码:
myset.find(x) != myset.end()
如何检查一个元素是否在集合中?
是否有与以下代码更简单的等效代码:
myset.find(x) != myset.end()
当前回答
我使用
if(!my_set.count(that_element)) //Element is present...
;
但它的效率不如
if(my_set.find(that_element)!=my_set.end()) ....;
我的版本只是节省了我写代码的时间。对于竞争性编码,我更喜欢这种方式。
其他回答
Just to clarify, the reason why there is no member like contains() in these container types is because it would open you up to writing inefficient code. Such a method would probably just do a this->find(key) != this->end() internally, but consider what you do when the key is indeed present; in most cases you'll then want to get the element and do something with it. This means you'd have to do a second find(), which is inefficient. It's better to use find directly, so you can cache your result, like so:
auto it = myContainer.find(key);
if (it != myContainer.end())
{
// Do something with it, no more lookup needed.
}
else
{
// Key was not present.
}
当然,如果你不关心效率,你总是可以自己滚动,但在这种情况下,你可能不应该使用c++…;)
/ /通用语法
set<int>::iterator ii = find(set1.begin(),set1.end(),"element to be searched");
/*在下面的代码中,我试图找到元素4和int集,如果它存在与否*/
set<int>::iterator ii = find(set1.begin(),set1.end(),4);
if(ii!=set1.end())
{
cout<<"element found";
set1.erase(ii);// in case you want to erase that element from set.
}
检查许多STL容器是否存在的典型方法,如std::map, std::set,…是:
const bool is_in = container.find(element) != container.end();
写你自己的:
template<class T>
bool checkElementIsInSet(const T& elem, const std::set<T>& container)
{
return container.find(elem) != container.end();
}
从c++ 20开始,就有了bool std::contains(const K&) https://en.cppreference.com/w/cpp/container/set/contains