std::ranges::set_difference, std::ranges::set_difference_result
| 定義於標頭檔案 <algorithm> |
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| 呼叫簽名 (Call signature) |
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| template< std::input_iterator I1, std::sentinel_for<I1> S1, std::input_iterator I2, std::sentinel_for<I2> S2, |
(1) | (C++20 起) |
| template< ranges::input_range R1, ranges::input_range R2, std::weakly_incrementable O, class Comp = ranges::less, |
(2) | (C++20 起) |
| 輔助型別 |
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| template< class I, class O > using set_difference_result = ranges::in_out_result<I, O>; |
(3) | (C++20 起) |
將來自已排序輸入範圍 [first1, last1) 中未在已排序輸入範圍 [first2, last2) 中找到的元素複製到始於 result 的輸出範圍。
若出現以下情況，行為未定義：
- 輸入範圍分別未根據 comp 和 proj1 或 proj2 排序，或
- 結果範圍與任一輸入範圍重疊。
本頁描述的類函式實體是 演算法函式物件（非正式地稱為 niebloids），即
目錄 |
[編輯] 引數
| first1, last1 | - | 定義第一個已排序輸入範圍元素的迭代器-哨兵對 |
| first2, last2 | - | 定義第二個已排序輸入範圍元素的迭代器-哨兵對 |
| r1 | - | 第一個已排序的輸入範圍 |
| r2 | - | 第二個已排序的輸入範圍 |
| result | - | 輸出範圍的起始 |
| comp | - | 應用於投影元素的比較器 |
| proj1 | - | 應用於第一個範圍元素的投影。 |
| proj2 | - | 應用於第二個範圍元素的投影。 |
[編輯] 返回值
{last1, result_last}，其中 result_last 是已構造範圍的末尾。
[編輯] 複雜度
至多進行 2·(N1+N2)-1 次比較和每個投影的應用，其中 N1 和 N2 分別是 ranges::distance(first1, last1) 和 ranges::distance(first2, last2)。
[編輯] 可能的實現
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 {}; |
[編輯] 示例
#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 // a struct with some very interesting data { 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\n"); // We want to know which orders "cut" between old and new states: 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"); }
輸出
{ 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} }[編輯] 參閱
| (C++20) |
計算兩個集合的並集 (演算法函式物件) |
| (C++20) |
計算兩個集合的交集 (演算法函式物件) |
| 計算兩個集合的對稱差 (演算法函式物件) | |
| (C++20) |
如果一個序列是另一個序列的子序列，則返回 true (演算法函式物件) |
| 計算兩個集合的差集 (函式模板) |
