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C++ Set 中的 upper_bound函数

C++ set upper_bound()函数用于返回一个迭代器，该迭代器指向set集合中的值，该值大于参数中传递的val。

upper_bound - 语法

iterator upper_bound (const value_type& val) const;            //until C++ 11
iterator upper_bound (const value_type& val);                    //since C++ 11
const_iterator upper_bound (const value_type& val) const;        //since C++ 11

upper_bound - 参数

val :要在设置的集合中搜索的值。

upper_bound - 返回值

它返回一个指向设置集合中值的迭代器，该值大于参数中传递的val。如果没有这样的元素，则返回end()。

upper_bound - 例子1

让我们看一个简单的示例，以获取给定值的上限:

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 it = m.upper_bound('b');

   cout << "Upper bound of b is(>): " << *it << endl;

   return 0;
}

输出:

Upper bound of b is(>): c

在上面的示例中，当我们尝试找到元素b的上限时，它将返回元素b的较大值，即c

upper_bound - 例子2

让我们看一个简单的示例，从下限到上限擦除set的元素:

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复制代码

#include <iostream>
#include <set>

using namespace std;

int main ()
{
  set<int> myset;
  set<int>::iterator itlow,itup;

  for (int i=1; i<10; i++) myset.insert(i*10);//10 20 30 40 50 60 70 80 90

  itlow=myset.lower_bound (30);               //      ^
  itup=myset.upper_bound (60);                //                  ^

  myset.erase(itlow,itup);                    //10 20 70 80 90

  std::cout << "myset contains:";
  for (set<int>::iterator it=myset.begin(); it!=myset.end(); ++it)
    cout << ' ' << *it;
  cout << '\n';

  return 0;
}

输出:

myset contains: 10 20 70 80 90

在上面的示例中，delete()函数将set的元素从下限(=)擦除到上限(>)，并打印其余内容。

upper_bound - 例子3

让我们看一个简单的例子:

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( 12 );
    mp.insert( 11 );
    mp.insert( 15 );
    mp.insert( 14 );
 
   //when 11 is present
    auto it = mp.upper_bound(11);
    cout << "The upper bound of key 11 is ";
    cout << (*it)<< endl;
 
   //when 13 is not present
    it = mp.upper_bound(13);
    cout << "The upper bound of key 13 is ";
    cout << (*it)<< endl;
 
   //when 17 is exceeds the maximum key, so size
       //of mp is returned as key and value as 0.
    it = mp.upper_bound(17);
    cout << "The upper bound of key 17 is ";
    cout << (*it);
    return 0;
}

输出:

The upper bound of key 11 is 12
The upper bound of key 13 is 14
The upper bound of key 17 is 4

在上面的示例中，当我们尝试找到不存在于集合集合中但未超过最大值的值的上限时，它将返回更大的值，即当我们尝试找到13的上限时，它将返回返回14，当我们尝试查找集合中不存在且超过集合最大值的值的上限时，它将返回到end()。

upper_bound - 例子4

让我们看一个简单的例子:

在线运行复制代码

#include <set>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;     
   set <int> s1;  
   set <int> :: const_iterator s1_AcIter, s1_RcIter;  
  
   s1.insert( 10 );  
   s1.insert( 20 );  
   s1.insert( 30 );  
  
   s1_RcIter = s1.upper_bound( 20 );  
   cout << "The first element of set s1 with a key greater "  
        << "than 20 is: " << *s1_RcIter << "." << endl;  
  
   s1_RcIter = s1.upper_bound( 30 );  
  
  //If no match is found for the key, end( ) is returned  
   if ( s1_RcIter == s1.end( ) )  
      cout << "The set s1 doesn't have an element "  
           << "with a key greater than 30." << endl;  
   else  
      cout << "The element of set s1 with a key > 40 is: "  
           << *s1_RcIter << "." << endl;  
  
  //The element at a specific location in the set can be found   
  //by using a dereferenced iterator addressing the location  
   s1_AcIter = s1.begin( );  
   s1_RcIter = s1.upper_bound( *s1_AcIter );  
   cout << "The first element of s1 with a key greater than"  
        << endl << "that of the initial element of s1 is: "  
        << *s1_RcIter << "." << endl;  
        
        return 0;
}

输出:

The first element of set s1 with a key greater than 20 is: 30.
The set s1 doesn't have an element with a key greater than 30.
The first element of s1 with a key greater than
that of the initial element of s1 is: 20.

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