C++ STL中的multiset lower_bound()及示例

multiset::lower_bound() 是C++ STL中的内置函数，它返回指向容器中等于参数k的第一个元素的迭代器。如果k不在集合容器中，则该函数返回一个指向比k大的第一个立即后继元素的迭代器。如果参数中的键超过容器中的最大值，则返回迭代器打印容器中的元素数量。

语法：

multiset_name.lower_bound(key)

参数： 此函数接受一个单一的强制性参数key，它指定要返回其lower_bound的元素。

返回值： 该函数返回一个迭代器。

下面的程序说明了以上功能：

程序1：

// CPP program to demonstrate the
// multiset::lower_bound() function
#include <bits/stdc++.h>
using namespace std;
int main()
{
    multiset<int> 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;
}

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

程序2：

// CPP program to demonstrate the
// multiset::lower_bound() function
#include <bits/stdc++.h>
using namespace std;
int main()
{
    multiset<int> 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;
}

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