std::ranges::set_difference, std::ranges::set_difference_result
来自cppreference.com
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| 在标头 <algorithm> 定义
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| 调用签名 |
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template< std::input_iterator I1, std::sentinel_for<I1> S1, std::input_iterator I2, std::sentinel_for<I2> S2, std::weakly_incrementable O, class Comp = ranges::less, class Proj1 = std::identity, class Proj2 = std::identity > requires std::mergeable<I1, I2, O, Comp, Proj1, Proj2> constexpr set_difference_result<I1, O> set_difference( I1 first1, S1 last1, I2 first2, S2 last2, O result, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {} ); |
(1) | (C++20 起) |
template< ranges::input_range R1, ranges::input_range R2, std::weakly_incrementable O, class Comp = ranges::less, class Proj1 = std::identity, class Proj2 = std::identity > requires std::mergeable<ranges::iterator_t<R1>, ranges::iterator_t<R2>, O, Comp, Proj1, Proj2> constexpr set_difference_result<ranges::borrowed_iterator_t<R1>, O> set_difference( R1&& r1, R2&& r2, O result, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {} ); |
(2) | (C++20 起) |
| 辅助类型 |
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template< class I, class O > using set_difference_result = ranges::in_out_result<I, O>; |
(3) | (C++20 起) |
从有序输入范围 [first1, last1) 将在有序输入范围 [first2, last2) 中找不到的元素赋值到始于 result 的输出范围。
若
- 输入范围未分别相对于
comp与proj1或proj2排序，或 - 结果范围与任一输入范围重叠，
则行为未定义。
1) 用给定的二元比较函数
comp 比较元素。2) 同 (1)，但以
r1 为第一范围，并以 r2 为第二范围，如同以 ranges::begin(r1) 为 first1，以 ranges::end(r1) 为 last1，以 ranges::begin(r2) 为 first2，并以 ranges::end(r2) 为 last2。此页面上描述的函数式实体是算法函数对象（非正式地称为 niebloid），即：
参数
| first1, last1 | - | 第一个输入的有序元素范围的迭代器-哨位对 |
| first2, last2 | - | 第二个输入的有序元素范围的迭代器-哨位对 |
| r1 | - | 第一个输入的有序范围 |
| r2 | - | 第二个输入的有序范围 |
| result | - | 输出范围的起始 |
| comp | - | 应用到投影后元素的比较器 |
| proj1 | - | 应用到第一个范围元素的投影 |
| proj2 | - | 应用到第二个范围元素的投影 |
返回值
{last1, result_last}，其中 result_last 为被构造范围末尾。
复杂度
至多比较和应用每个投影 2·(N1+N2)-1 次，其中 N1 与 N2 分别为 ranges::distance(first1, last1) 与 ranges::distance(first2, last2)。
可能的实现
struct set_difference_fn
{
template<std::input_iterator I1, std::sentinel_for<I1> S1,
std::input_iterator I2, std::sentinel_for<I2> S2,
std::weakly_incrementable O, class Comp = ranges::less,
class Proj1 = std::identity, class Proj2 = std::identity>
requires std::mergeable<I1, I2, O, Comp, Proj1, Proj2>
constexpr ranges::set_difference_result<I1, O>
operator()(I1 first1, S1 last1, I2 first2, S2 last2,
O result, Comp comp = {},
Proj1 proj1 = {}, Proj2 proj2 = {}) const
{
while (!(first1 == last1 or first2 == last2))
{
if (std::invoke(comp, std::invoke(proj1, *first1), std::invoke(proj2, *first2)))
{
*result = *first1;
++first1;
++result;
}
else if (std::invoke(comp, std::invoke(proj2, *first2),
std::invoke(proj1, *first1)))
++first2;
else
{
++first1;
++first2;
}
}
return ranges::copy(std::move(first1), std::move(last1), std::move(result));
}
template<ranges::input_range R1, ranges::input_range R2,
std::weakly_incrementable O, class Comp = ranges::less,
class Proj1 = std::identity, class Proj2 = std::identity>
requires std::mergeable<ranges::iterator_t<R1>, ranges::iterator_t<R2>,
O, Comp, Proj1, Proj2>
constexpr ranges::set_difference_result<ranges::borrowed_iterator_t<R1>, O>
operator()(R1&& r1, R2&& r2, O result, Comp comp = {},
Proj1 proj1 = {}, Proj2 proj2 = {}) const
{
return (*this)(ranges::begin(r1), ranges::end(r1),
ranges::begin(r2), ranges::end(r2),
std::move(result), std::move(comp),
std::move(proj1), std::move(proj2));
}
};
inline constexpr set_difference_fn set_difference {};
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示例
运行此代码
#include <algorithm>
#include <cassert>
#include <iostream>
#include <iterator>
#include <string_view>
#include <vector>
auto print = [](const auto& v, std::string_view end = "")
{
std::cout << "{ ";
for (auto n{v.size()}; auto i : v)
std::cout << i << (--n ? ", " : " ");
std::cout << "} " << end;
};
struct Order // 拥有非常有趣的数据的类
{
int order_id{};
friend std::ostream& operator<<(std::ostream& os, const Order& ord)
{
return os << '{' << ord.order_id << '}';
}
};
int main()
{
const auto v1 = {1, 2, 5, 5, 5, 9};
const auto v2 = {2, 5, 7};
std::vector<int> diff;
std::ranges::set_difference(v1, v2, std::back_inserter(diff));
print(v1, "∖ ");
print(v2, "= ");
print(diff, "\n");
// 我们想知道哪些顺序在旧和新状态之间“改变了”：
const std::vector<Order> old_orders{{1}, {2}, {5}, {9}};
const std::vector<Order> new_orders{{2}, {5}, {7}};
std::vector<Order> cut_orders(old_orders.size() + new_orders.size());
auto [old_orders_end, cut_orders_last] =
std::ranges::set_difference(old_orders, new_orders,
cut_orders.begin(), {},
&Order::order_id, &Order::order_id);
assert(old_orders_end == old_orders.end());
std::cout << "old orders = ";
print(old_orders, "\n");
std::cout << "new orders = ";
print(new_orders, "\n");
std::cout << "cut orders = ";
print(cut_orders, "\n");
cut_orders.erase(cut_orders_last, end(cut_orders));
std::cout << "cut orders = ";
print(cut_orders, "\n");
}
输出：
{ 1, 2, 5, 5, 5, 9 } ∖ { 2, 5, 7 } = { 1, 5, 5, 9 }
old orders = { {1}, {2}, {5}, {9} }
new orders = { {2}, {5}, {7} }
cut orders = { {1}, {9}, {0}, {0}, {0}, {0}, {0} }
cut orders = { {1}, {9} }
参阅
(C++20) |
计算两个集合的并集 (算法函数对象) |
(C++20) |
计算两个集合的交集 (算法函数对象) |
| 计算两个集合的对称差 (算法函数对象) | |
(C++20) |
当一个序列是另一个的子序列时返回 true (算法函数对象) |
| 计算两个集合的差集 (函数模板) |