关注我们

C++ Set 中的 equal_range函数

C++ set equal_range()函数用于返回包含集合中等于val的所有元素的参数的边界。由于set集合中没有值的重复项，因此此参数最多包含一个元素。

如果val与集合中的任何值都不匹配，则返回值参数将为长度0，并且两个迭代器均指向大于val的最近值。否则，如果val大于集合中的所有元素，则它指向end。

equal_range - 语法

pair<const_iterator,const_iterator> equal_range (const value_type& val) const;
pair<iterator,iterator> equal_range (const value_type& val);

该参数由两个迭代器定义，一个指向不小于val的第一个元素，另一个指向大于val的第一个元素。

equal_range - 参数

val :要在设置的集合中搜索的值。

equal_range - 返回值

该函数返回pair。其中pair :: first位于参数的下边界，具有与lower_bound(val)将返回的值相同的值，pair :: second是与upper_bound(val)将返回的值相同，它对应的参数的上限。

equal_range - 例子1

让我们看一个简单的例子:

链接：https://www.learnfk.comhttps://www.learnfk.com/c++/cpp-set-equal-range-function.html

来源：LearnFk无涯教程网

在线运行复制代码

#include <iostream>
#include <set>

using namespace std;

int main(void) {
   set<char> m = {'a','b','c','d'};

   auto ret = m.equal_range('b');

   cout << "Lower bound of b is: " << *ret.first<< endl;

   cout << "Upper bound of b is: " << *ret.second<< endl;

   return 0;
}

输出:

Lower bound of b is: b
Upper bound of b is: c

在上面的示例中，b的下限为b，b的上限为c。

equal_range - 例子2

让我们看一个简单的例子:

链接：https://www.learnfk.comhttps://www.learnfk.com/c++/cpp-set-equal-range-function.html

来源：LearnFk无涯教程网

在线运行复制代码

#include <iostream>
#include <set>

using namespace std;
 
int main()
{
    //initialize container
    set<int> mp;
 
   //insert elements in random order
    mp.insert( 4 );
    mp.insert( 1 );
    mp.insert( 6 );
 
    pair<set<int>::const_iterator,set<int>::const_iterator> ret;
 
    ret = mp.equal_range(10);
    cout << "The lower bound is: " << *ret.first;
    cout << "\nThe upper bound is: " << *ret.second;
 
    return 0;
}

输出:

The lower bound is 3
The upper bound is 3

在上面的示例中，equal_range()函数返回到end()即3，因为它试图查找集合mp中不存在的10。

equal_range - 例子3

让我们看一个简单的例子:

链接：https://www.learnfk.comhttps://www.learnfk.com/c++/cpp-set-equal-range-function.html

来源：LearnFk无涯教程网

在线运行复制代码

#include <set>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
   typedef set<int, less< int > > IntSet;  
   IntSet s1;  
   set <int, less< int > > :: const_iterator s1_RcIter;  
  
   s1.insert( 10 );  
   s1.insert( 20 );  
   s1.insert( 30 );  
  
   pair <IntSet::const_iterator, IntSet::const_iterator> p1, p2;  
   p1 = s1.equal_range( 20 );  
  
   cout << "The upper bound of the element with "  
        << "a key of 20 in the set s1 is: "  
        << *(p1.second) << "." << endl;  
  
   cout << "The lower bound of the element with "  
        << "a key of 20 in the set s1 is: "  
        << *(p1.first) << "." << endl;  
  
  //Compare the upper_bound called directly   
   s1_RcIter = s1.upper_bound( 20 );  
   cout << "A direct call of upper_bound( 20 ) gives "  
        << *s1_RcIter << "," << endl  
        << "matching the 2nd element of the pair"  
        << " returned by equal_range( 20 )." << endl;  
  
   p2 = s1.equal_range( 40 );  
  
  //If no match is found for the key,  
  //both elements of the pair return end( )  
   if ( ( p2.first == s1.end( ) ) && ( p2.second == s1.end( ) ) )  
      cout << "The set s1 doesn't have an element "  
           << "with a key less than 40." << endl;  
   else  
      cout << "The element of set s1 with a key >= 40 is: "  
           << *(p1.first) << "." << endl; 
           
           return 0;
}

输出:

The upper bound of the element with a key of 20 in the set s1 is: 30.
The lower bound of the element with a key of 20 in the set s1 is: 20.
A direct call of upper_bound( 20 ) gives 30,
matching the 2nd element of the pair returned by equal_range( 20 ).
The set s1 doesn't have an element with a key less than 40.

equal_range - 例子4

让我们看一个简单的例子:

复制代码

#include <iostream>
#include <set>

using namespace std;

int main ()
{
  std::set<int> myset;

  for (int i=1; i<=5; i++) myset.insert(i*10);  //myset: 10 20 30 40 50

  pair<std::set<int>::const_iterator,set<int>::const_iterator> ret;
  ret = myset.equal_range(30);

  cout << "The lower bound points to: " << *ret.first << '\n';
  cout << "The upper bound points to: " << *ret.second << '\n';

  return 0;
}

输出:

The lower bound points to: 30
The upper bound points to: 40

祝学习愉快！(内容编辑有误？请选中要编辑内容 -> 右键 -> 修改 -> 提交！)

技术教程推荐

技术与商业案例解读 -〔徐飞〕

软件测试52讲 -〔茹炳晟〕

TensorFlow快速入门与实战 -〔彭靖田〕

玩转webpack -〔程柳锋〕

设计模式之美 -〔王争〕

架构实战案例解析 -〔王庆友〕

Selenium自动化测试实战 -〔郭宏志〕

手把手带你搭建推荐系统 -〔黄鸿波〕

云时代的JVM原理与实战 -〔康杨〕

好记忆不如烂笔头。留下您的足迹吧 :)