C++ 标准库 已排序区间算法

本文深入探讨了C++标准库中针对已排序区间的算法,包括std::binary_search、std::includes、std::lower_bound等,并通过具体示例展示了它们的功能与使用方法。

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一 概述
  • C++ 标准库中提供了很多算法,定义于头文件 < algorithm >。本文主要探究以下用于 已排序区间 的算法:
    • std::binary_search 查找元素是否存在于某范围中
    • std::includes 范围是否包含另一范围
    • std::lower_bound 返回指向第一个不小于给定值的元素的迭代器
    • std::upper_bound 返回指向第一个大于给定值的元素的迭代器
    • std::equal_range 返回匹配特定键值的元素范围
    • std::merge 归并两个已排序区间到一个已排序区间
    • std::set_union 计算并集
    • std::set_intersection 计算交集
    • std::set_difference 计算差集
    • std::set_symmetric_difference 计算对称差
    • std::inplace_merge 归并两个相继已排序区间到一个排序区间(稳定排序)
    • std::partition_point 定位已划分范围的划分点
二 辅助函数
三 std::binary_search
  • 定义
template< class ForwardIt, class T >
bool binary_search( ForwardIt first, ForwardIt last, const T& value );(1)(until C++20)
template< class ForwardIt, class T >
constexpr bool binary_search( ForwardIt first, ForwardIt last, const T& value );(1)(since C++20)
template< class ForwardIt, class T, class Compare >
bool binary_search( ForwardIt first, ForwardIt last, const T& value, Compare comp );(2)(until C++20)
template< class ForwardIt, class T, class Compare >
constexpr bool binary_search( ForwardIt first, ForwardIt last, const T& value, 
                              Compare comp );(2)(since C++20)
  • Demo
if (1) {
  // std::binary_search 查找元素是否存在于某范围中
  std::vector<int> vc;
  fill(vc, 1, 6);
  print("vc: ", vc);
  std::cout << "find 6 in vc: " << std::boolalpha << std::binary_search(vc.begin(), vc.end(), 6) << std::endl;
  std::cout << "find 7 in vc: " << std::boolalpha << std::binary_search(vc.begin(), vc.end(), 7) << std::endl;
}
  • 结果
vc: 1 2 3 4 5 6
find 6 in vc: true
find 7 in vc: false
四 std::includes
  • 定义
template< class InputIt1, class InputIt2 >
bool includes( InputIt1 first1, InputIt1 last1,
               InputIt2 first2, InputIt2 last2 );(1)(until C++20)
template< class InputIt1, class InputIt2 >
constexpr bool includes( InputIt1 first1, InputIt1 last1,
                         InputIt2 first2, InputIt2 last2 );(1)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 >
bool includes( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1,
               ForwardIt2 first2, ForwardIt2 last2 );(2)(since C++17)	
template< class InputIt1, class InputIt2, class Compare >
bool includes( InputIt1 first1, InputIt1 last1,
               InputIt2 first2, InputIt2 last2, Compare comp );(3)(until C++20)
template< class InputIt1, class InputIt2, class Compare >
constexpr bool includes( InputIt1 first1, InputIt1 last1,
                         InputIt2 first2, InputIt2 last2, Compare comp );(3)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class Compare >
bool includes( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1,
               ForwardIt2 first2, ForwardIt2 last2, Compare comp );(4)(since C++17)
if (1) {
  // std::includes 范围是否包含另一范围
  std::vector<int> vc;
  fill(vc, 1, 6);
  std::vector<int> vc1;
  fill(vc1, 2, 4);
  std::vector<int> vc2;
  fill(vc2, 3, 7);
  print("vc: ", vc);
  print("vc1: ", vc1);
  print("vc2: ", vc2);
  std::cout << "vc1 in vc: " << std::boolalpha
  << std::includes(vc.begin(), vc.end(), vc1.begin(), vc1.end()) << std::endl;
  std::cout << "vc2 in vc: " << std::boolalpha
  << std::includes(vc.begin(), vc.end(), vc2.begin(), vc2.end()) << std::endl;
}
  • 结果
vc: 1 2 3 4 5 6
vc1: 2 3 4
vc2: 3 4 5 6 7
vc1 in vc: true
vc2 in vc: false
五 std::lower_bound
  • 定义
template< class ForwardIt, class T >
ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value );(1)
(until C++20)
template< class ForwardIt, class T >
constexpr ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value );(1)
(since C++20)
template< class ForwardIt, class T, class Compare >
ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value, Compare comp );(2)
(until C++20)
template< class ForwardIt, class T, class Compare >
constexpr ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value, 
                                 Compare comp );(2)(since C++20)
  • Demo
if (1) {
  // std::lower_bound 返回指向第一个不小于给定值的元素的迭代器
  std::vector<int> vc{1,3,5,7};
  print("vc: ", vc);
  std::cout << "lower_bound 5 in vc: "
            << *std::lower_bound(vc.begin(), vc.end(), 5) << std::endl;
}
  • 结果
vc: 1 3 5 7
lower_bound 5 in vc: 5
六 std::upper_bound
  • 定义
template< class ForwardIt, class T >
ForwardIt upper_bound( ForwardIt first, ForwardIt last, const T& value );(1)(until C++20)
template< class ForwardIt, class T >
constexpr ForwardIt upper_bound( ForwardIt first, ForwardIt last, const T& value );(1)(since C++20)	
template< class ForwardIt, class T, class Compare >
ForwardIt upper_bound( ForwardIt first, ForwardIt last, const T& value, 
                       Compare comp );(2)(until C++20)
template< class ForwardIt, class T, class Compare >
constexpr ForwardIt upper_bound( ForwardIt first, ForwardIt last, const T& value, 
                                 Compare comp );(2)(since C++20)
  • Demo
if (1) {
  // std::upper_bound 返回指向第一个大于给定值的元素的迭代器
  std::vector<int> vc{1, 3, 5, 7};
  print("vc: ", vc);
  std::cout << "upper_bound 5 in vc: "
            << *std::upper_bound(vc.begin(), vc.end(), 5) << std::endl;
}
  • 结果
vc: 1 3 5 7
upper_bound 5 in vc: 7
七 std::equal_range
  • 定义
template< class ForwardIt, class T >
std::pair<ForwardIt,ForwardIt>
    equal_range( ForwardIt first, ForwardIt last,
                 const T& value );(1)(until C++20)
template< class ForwardIt, class T >
constexpr std::pair<ForwardIt,ForwardIt>
    equal_range( ForwardIt first, ForwardIt last,
                           const T& value );(1)(since C++20)
template< class ForwardIt, class T, class Compare >
std::pair<ForwardIt,ForwardIt>
    equal_range( ForwardIt first, ForwardIt last,
                 const T& value, Compare comp );(2)(until C++20)
template< class ForwardIt, class T, class Compare >
constexpr std::pair<ForwardIt,ForwardIt>
    equal_range( ForwardIt first, ForwardIt last,
                 const T& value, Compare comp );(2)(since C++20)
  • Demo
if (1) {
  // std::equal_range 返回匹配特定键值的元素范围
  std::vector<int> vc{1, 3, 5, 7};
  print("vc: ", vc);
  auto p = std::equal_range(vc.begin(), vc.end(), 5);
  std::cout << "equal_range 5 in vc first pos: "
            << std::distance(vc.begin(), p.first) << std::endl;
  std::cout << "equal_range 5 in vc end pos: "
            << std::distance(vc.begin(), p.second) << std::endl;
}
  • 结果
equal_range 5 in vc first pos: 2
equal_range 5 in vc end pos: 3
八 std::merge
  • 定义
template< class InputIt1, class InputIt2, class OutputIt >
OutputIt merge( InputIt1 first1, InputIt1 last1,
                InputIt2 first2, InputIt2 last2,
                OutputIt d_first );(1)(until C++20)
template< class InputIt1, class InputIt2, class OutputIt >
constexpr OutputIt merge( InputIt1 first1, InputIt1 last1,
                          InputIt2 first2, InputIt2 last2,
                          OutputIt d_first );(1)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class ForwardIt3 >
ForwardIt3 merge( ExecutionPolicy&& policy,
                  ForwardIt1 first1, ForwardIt1 last1,
                  ForwardIt2 first2, ForwardIt2 last2,
                  ForwardIt3 d_first );(2)(since C++17)	
template< class InputIt1, class InputIt2, class OutputIt, class Compare>
OutputIt merge( InputIt1 first1, InputIt1 last1,
                InputIt2 first2, InputIt2 last2,
                OutputIt d_first, Compare comp );(3)(until C++20)
template< class InputIt1, class InputIt2, class OutputIt, class Compare>
constexpr OutputIt merge( InputIt1 first1, InputIt1 last1,
                          InputIt2 first2, InputIt2 last2,
                          OutputIt d_first, Compare comp );(3)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class ForwardIt3, class Compare>
ForwardIt3 merge( ExecutionPolicy&& policy,
                  ForwardIt1 first1, ForwardIt1 last1,
                  ForwardIt2 first2, ForwardIt2 last2,
                  ForwardIt3 d_first, Compare comp );(4)(since C++17)
  • Demo
if (1) {
  // std::merge 归并两个已排序区间到一个已排序区间
  std::vector<int> vc1{1, 3, 5, 7};
  print("vc1: ", vc1);
  std::vector<int> vc2{2, 4, 6, 8};
  print("vc2: ", vc2);
  std::vector<int> vc3;
  print("vc3: ", vc3);
  auto p = std::merge(vc1.begin(), vc1.end(), vc2.begin(), vc2.end(), std::back_inserter(vc3));
  std::cout << "merge vc1 and vc2 to vc3: "<< std::endl;
  print("vc3: ", vc3);
}
  • 结果
vc1: 1 3 5 7
vc2: 2 4 6 8
vc3:
merge vc1 and vc2 to vc3:
vc3: 1 2 3 4 5 6 7 8
九 std::set_union
  • 定义
template< class InputIt1, class InputIt2, class OutputIt >
OutputIt set_union( InputIt1 first1, InputIt1 last1,
                    InputIt2 first2, InputIt2 last2,
                    OutputIt d_first );(1)(until C++20)
template< class InputIt1, class InputIt2, class OutputIt >
constexpr OutputIt set_union( InputIt1 first1, InputIt1 last1,
                              InputIt2 first2, InputIt2 last2,
                              OutputIt d_first );(1)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class ForwardIt3 >
ForwardIt3 set_union( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1,
                    ForwardIt2 first2, ForwardIt2 last2,
                    ForwardIt3 d_first );(2)(since C++17)
template< class InputIt1, class InputIt2,
          class OutputIt, class Compare >
OutputIt set_union( InputIt1 first1, InputIt1 last1,
                    InputIt2 first2, InputIt2 last2,
                    OutputIt d_first, Compare comp );(3)(until C++20)
template< class InputIt1, class InputIt2,
          class OutputIt, class Compare >
constexpr OutputIt set_union( InputIt1 first1, InputIt1 last1,
                              InputIt2 first2, InputIt2 last2,
                              OutputIt d_first, Compare comp );(3)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
          class ForwardIt3, class Compare >
ForwardIt3 set_union( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1,
                    ForwardIt2 first2, ForwardIt2 last2,
                    ForwardIt3 d_first, Compare comp );(4)(since C++17)
  • Demo
if (1) {
  // std::set_union 计算并集
  std::vector<int> vc1{1, 3, 5, 7};
  print("vc1: ", vc1);
  std::vector<int> vc2{2, 4, 6, 8};
  print("vc2: ", vc2);
  std::vector<int> vc3;
  print("vc3: ", vc3);
  auto p = std::set_union(vc1.begin(), vc1.end(), vc2.begin(), vc2.end(),
                      std::back_inserter(vc3));
  std::cout << "set_union vc1 and vc2 to vc3: " << std::endl;
  print("vc3: ", vc3);
}
  • 结果
vc1: 1 3 5 7
vc2: 2 4 6 8
vc3:
set_union vc1 and vc2 to vc3:
vc3: 1 2 3 4 5 6 7 8
十 std::set_intersection
  • 定义
template< class InputIt1, class InputIt2, class OutputIt >
OutputIt set_intersection( InputIt1 first1, InputIt1 last1,
                           InputIt2 first2, InputIt2 last2,
                           OutputIt d_first );(1)(until C++20)
template< class InputIt1, class InputIt2, class OutputIt >
constexpr OutputIt set_intersection( InputIt1 first1, InputIt1 last1,
                                     InputIt2 first2, InputIt2 last2,
                                     OutputIt d_first );(1)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class ForwardIt3 >
ForwardIt3 set_intersection( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1,
                             ForwardIt2 first2, ForwardIt2 last2,
                             ForwardIt3 d_first );(2)(since C++17)
template< class InputIt1, class InputIt2,
          class OutputIt, class Compare >
OutputIt set_intersection( InputIt1 first1, InputIt1 last1,
                           InputIt2 first2, InputIt2 last2,
                           OutputIt d_first, Compare comp );(3)(until C++20)
template< class InputIt1, class InputIt2,
                    class OutputIt, class Compare >
constexpr OutputIt set_intersection( InputIt1 first1, InputIt1 last1,
                                     InputIt2 first2, InputIt2 last2,
                                     OutputIt d_first, Compare comp );(3)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
          class ForwardIt3, class Compare >
ForwardIt3 set_intersection( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1,
                             ForwardIt2 first2, ForwardIt2 last2,
                             ForwardIt3 d_first, Compare comp );(4)(since C++17)
  • Demo
if (1) {
  // std::set_intersection 计算交集
  std::vector<int> vc1{1, 2, 3, 5, 7};
  print("vc1: ", vc1);
  std::vector<int> vc2{2, 4, 6, 8};
  print("vc2: ", vc2);
  std::vector<int> vc3;
  print("vc3: ", vc3);
  auto p = std::set_intersection(vc1.begin(), vc1.end(), vc2.begin(), vc2.end(),
                      std::back_inserter(vc3));
  std::cout << "set_intersection vc1 and vc2 to vc3: " << std::endl;
  print("vc3: ", vc3);
}
  • 结果
vc1: 1 2 3 5 7
vc2: 2 4 6 8
vc3:
set_intersection vc1 and vc2 to vc3:
vc3: 2
十一 std::set_difference
  • 定义
template< class InputIt1, class InputIt2, class OutputIt >
OutputIt set_difference( InputIt1 first1, InputIt1 last1,
                         InputIt2 first2, InputIt2 last2,
                         OutputIt d_first );(1)(until C++20)
template< class InputIt1, class InputIt2, class OutputIt >
constexpr OutputIt set_difference( InputIt1 first1, InputIt1 last1,
                                   InputIt2 first2, InputIt2 last2,
                                   OutputIt d_first );(1)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class ForwardIt3 >
ForwardIt3 set_difference( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1,
                           ForwardIt2 first2, ForwardIt2 last2,
                           ForwardIt3 d_first );(2)(since C++17)	
template< class InputIt1, class InputIt2,
          class OutputIt, class Compare >
OutputIt set_difference( InputIt1 first1, InputIt1 last1,
                         InputIt2 first2, InputIt2 last2,
                         OutputIt d_first, Compare comp );(3)(until C++20)
template< class InputIt1, class InputIt2,
          class OutputIt, class Compare >
constexpr OutputIt set_difference( InputIt1 first1, InputIt1 last1,
                                   InputIt2 first2, InputIt2 last2,
                                   OutputIt d_first, Compare comp );(3)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
          class ForwardIt3, class Compare >
ForwardIt3 set_difference( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1,
                           ForwardIt2 first2, ForwardIt2 last2,
                           ForwardIt3 d_first, Compare comp );(4)(since C++17)
  • Demo
if (1) {
  // std::set_difference 计算差集
  std::vector<int> vc1{1, 2, 3, 5, 7};
  print("vc1: ", vc1);
  std::vector<int> vc2{2, 4, 6, 8};
  print("vc2: ", vc2);
  std::vector<int> vc3;
  print("vc3: ", vc3);
  auto p = std::set_difference(vc1.begin(), vc1.end(), vc2.begin(), vc2.end(),
                      std::back_inserter(vc3));
  std::cout << "set_difference vc1 and vc2 to vc3: " << std::endl;
  print("vc3: ", vc3);
}
  • 结果
vc1: 1 2 3 5 7
vc2: 2 4 6 8
vc3:
set_difference vc1 and vc2 to vc3:
vc3: 1 3 5 7
十二 std::set_symmetric_difference
  • 定义
template< class InputIt1, class InputIt2, class OutputIt >
OutputIt set_symmetric_difference( InputIt1 first1, InputIt1 last1,
                                   InputIt2 first2, InputIt2 last2,
                                   OutputIt d_first );(1)(until C++20)
template< class InputIt1, class InputIt2, class OutputIt >
constexpr OutputIt set_symmetric_difference( InputIt1 first1, InputIt1 last1,
                                             InputIt2 first2, InputIt2 last2,
                                             OutputIt d_first );(1)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class ForwardIt3 >
ForwardIt3 set_symmetric_difference( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1,
                                   ForwardIt2 first2, ForwardIt2 last2,
                                   ForwardIt3 d_first );(2)	(since C++17)
template< class InputIt1, class InputIt2,
          class OutputIt, class Compare >
OutputIt set_symmetric_difference( InputIt1 first1, InputIt1 last1,
                                   InputIt2 first2, InputIt2 last2,
                                   OutputIt d_first, Compare comp );(3)(until C++20)
template< class InputIt1, class InputIt2,
          class OutputIt, class Compare >
constexpr OutputIt set_symmetric_difference( InputIt1 first1, InputIt1 last1,
                                             InputIt2 first2, InputIt2 last2,
                                             OutputIt d_first, Compare comp );(3)(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
          class ForwardIt3, class Compare >
ForwardIt3 set_symmetric_difference( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1,
                                   ForwardIt2 first2, ForwardIt2 last2,
                                   ForwardIt3 d_first, Compare comp );(4)(since C++17)
  • Demo
if (1) {
  // std::set_symmetric_difference 计算对称差
  std::vector<int> vc1{1, 2, 3, 5, 7};
  print("vc1: ", vc1);
  std::vector<int> vc2{2, 4, 6, 8};
  print("vc2: ", vc2);
  std::vector<int> vc3;
  print("vc3: ", vc3);
  auto p = std::set_symmetric_difference(vc1.begin(), vc1.end(), vc2.begin(), vc2.end(),
                      std::back_inserter(vc3));
  std::cout << "set_symmetric_difference vc1 and vc2 to vc3: " << std::endl;
  print("vc3: ", vc3);
}
  • 结果
vc1: 1 2 3 5 7
vc2: 2 4 6 8
vc3:
set_symmetric_difference vc1 and vc2 to vc3:
vc3: 1 3 4 5 6 7 8
  • 说明
    • 数学上,两个集合的对称差是只属于其中一个集合,而不属于另一个集合的元素组成的集合。
十三 std::inplace_merge
  • 定义
template< class BidirIt >
void inplace_merge( BidirIt first, BidirIt middle, BidirIt last );(1)	
template< class ExecutionPolicy, class BidirIt >
void inplace_merge( ExecutionPolicy&& policy, BidirIt first, 
                    BidirIt middle, BidirIt last );(2)(since C++17)
template< class BidirIt, class Compare>
void inplace_merge( BidirIt first, BidirIt middle, BidirIt last, Compare comp );(3)	
template< class ExecutionPolicy, class BidirIt, class Compare>
void inplace_merge( ExecutionPolicy&& policy, BidirIt first, BidirIt middle, 
                    BidirIt last, Compare comp );(4)(since C++17)
  • Demo
if (1) {
  // std::inplace_merge 归并两个相继已排序区间到一个排序区间(稳定排序)
  std::vector<std::pair<int, string>> vc{
      {1, "tom"}, {3, "lee"}, {1, "john"}, {5, "kate"}};
  for(auto item : vc) {
    std::cout << "{" << item.first << ", " << item.second << "}" << std::endl;
  }
  std::inplace_merge(vc.begin(), vc.begin() + 2, vc.end());
  std::cout << "after inplace_merge: " << std::endl;
  for (auto item : vc) {
    std::cout << "{" << item.first << ", " << item.second << "}" << std::endl;
  }
} 
  • 结果
{1, tom}
{3, lee}
{1, john}
{5, kate}
after inplace_merge:
{1, john}
{1, tom}
{3, lee}
{5, kate}
十四 std::partition_point
  • 定义
template< class ForwardIt, class UnaryPredicate >
ForwardIt partition_point( ForwardIt first, ForwardIt last, 
                           UnaryPredicate p );(since C++11)(until C++20)
template< class ForwardIt, class UnaryPredicate >
constexpr ForwardIt partition_point( ForwardIt first, ForwardIt last, 
                                     UnaryPredicate p );(since C++20)
  • Demo
if (1) {
  // std::partition_point 定位已划分范围的划分点
  std::vector<int> vc;
  fill(vc, 1, 6);
  print("vc: ", vc);
  std::partition(vc.begin(), vc.end(), even);
  print("vc: ", vc);
  auto it = std::partition_point(vc.begin(), vc.end(), even);
  std::cout << "partition_point vc of noteven: " << std::distance(vc.begin(), it)
            << std::endl;
}
  • 结果
vc: 1 2 3 4 5 6
vc: 6 2 4 3 5 1
partition_point vc of noteven: 3
十五 github
  • 所有Demo 已上传github cplusplus
  • sorted-range_algorithm.cpp
十六 参考
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