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multiset lower_bound() in C++ STL with Examples
  • Difficulty Level : Easy
  • Last Updated : 23 Jul, 2018

The multiset::lower_bound() is a built-in function in C++ STL which returns an iterator pointing to the first element in the container which is equivalent to k passed in the parameter. In case k is not present in the set container, the function returns an iterator pointing to the immediate next element which is just greater than k. If the key passed in the parameter exceeds the maximum value in the container, then the iterator returned prints the number of elements in the container.

Syntax:

multiset_name.lower_bound(key)

Parameters: This function accepts a single mandatory parameter key which specifies the element whose lower_bound is to be returned.

Return Value: The function returns an iterator.

Below program illustrate the above function:



Program 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;
}
Output:
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

Program 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;
}
Output:
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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