C++ STL中的多集lower_bound()示例

multiset :: lower_bound()是C++ STL中的内置函数，该函数返回一个迭代器，该迭代器指向容器中的第一个元素，该元素等效于在参数中传递的k。如果set容器中不存在k，则该函数返回一个迭代器，该迭代器指向刚好大于k的紧邻的下一个元素。如果传递给参数的键超过了容器中的最大值，则返回的迭代器将打印容器中的元素数。

句法：

multiset_name.lower_bound(key)

参数：此函数接受单个强制性参数键，该键指定要返回其lower_bound的元素。

返回值：该函数返回一个迭代器。

下面的程序说明了上述函数：

程序1：

// CPP program to demonstrate the
// multiset::lower_bound() function
#include 
using namespace std;
int main()
{
  
    multiset s;
  
    // Function to insert elements
    // in the multiset container
    s.insert(1);
    s.insert(2);
    s.insert(2);
    s.insert(1);
    s.insert(4);
  
    cout << "The multiset elements are: ";
    for (auto it = s.begin(); it != s.end(); it++)
        cout << *it << " ";
  
    // when 2 is present
    auto it = s.lower_bound(2);
    cout << "\nThe lower bound of key 2 is ";
    cout << (*it) << endl;
  
    // when 3 is not present
    // points to next greater after 3
    it = s.lower_bound(3);
    cout << "The lower bound of key 3 is ";
    cout << (*it) << endl;
  
    // when 5 exceeds the max element in multiset
    it = s.lower_bound(7);
    cout << "The lower bound of key 7 is ";
    cout << (*it) << endl;
  
    return 0;
}

输出：

The multiset elements are: 1 1 2 2 4 
The lower bound of key 2 is 2
The lower bound of key 3 is 4
The lower bound of key 7 is 5

程式2：

// CPP program to demonstrate the
// multiset::lower_bound() function
#include 
using namespace std;
int main()
{
  
    multiset s;
  
    // Function to insert elements
    // in the multiset container
    s.insert(1);
    s.insert(3);
    s.insert(3);
    s.insert(5);
    s.insert(4);
  
    cout << "The multiset elements are: ";
    for (auto it = s.begin(); it != s.end(); it++)
        cout << *it << " ";
  
    // when 3 is present
    auto it = s.lower_bound(3);
    cout << "\nThe lower bound of key 3 is ";
    cout << (*it) << endl;
  
    // when 2 is not present
    // points to next greater after 2
    it = s.lower_bound(2);
    cout << "The lower bound of key 2 is ";
    cout << (*it) << endl;
  
    // when 10 exceeds the max element in multiset
    it = s.lower_bound(10);
    cout << "The lower bound of key 10 is ";
    cout << (*it) << endl;
  
    return 0;
}

输出：

The multiset elements are: 1 3 3 4 5 
The lower bound of key 3 is 3
The lower bound of key 2 is 3
The lower bound of key 10 is 5

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