std::erase_if (std::unordered_set)

来自cppreference.com

 
 
 
 
在标头 <unordered_set> 定义
template< class Key, class Hash, class KeyEqual, class Alloc, class Pred >

typename std::unordered_set<Key, Hash, KeyEqual, Alloc>::size_type

    erase_if(std::unordered_set<Key, Hash, KeyEqual, Alloc>& c, Pred pred);
(C++20 起)

从容器中擦除所有满足谓词 pred 的元素。等价于

auto old_size = c.size();
for (auto i = c.begin(), last = c.end(); i != last; ) {
  if (pred(*i)) {
    i = c.erase(i);
  } else {
    ++i;
  }
}
return old_size - c.size();

参数

c - 要从中擦除的元素
pred - 若应该擦除元素则对它返回 true 的谓词

返回值

擦除的元素数。

复杂度

线性。

示例

#include <unordered_set>
#include <iostream>
 
template<typename Os, typename Container>
inline Os& operator<<(Os& os, Container const& container)
{
    os << "{ ";
    for (const auto& item : container) {
        os << item << ' ';
    }
    return os << "}";
}
 
int main()
{
    std::unordered_set data { 0, 1, 2, 3, 3, 4, 5, 5, 6, 6, 7 };
    std::cout << "Original:\n" << data << '\n';
 
    auto divisible_by_3 = [](auto const& x) { return (x % 3) == 0; };
 
    const auto count = std::erase_if(data, divisible_by_3);
 
    std::cout << "Erase all items divisible by 3:\n" << data << '\n'
              << count << " items erased.\n";
}

输出:

Original:
{ 7 6 5 4 3 2 1 0 }
Erase all items divisible by 3:
{ 7 5 4 2 1 }
3 items erased.

参阅

移除满足特定判别标准的元素
(函数模板)