Lower bound and upper bound of C++

Jimmy (xiaoke) Shen

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Feb 4, 2020

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Lower bound and upper bound in STL

• upper_bound() and lower_bound() are standard library functions in C++.
• upper_bound() returns an iterator pointing to the first element in the range [first, last) that is greater than the value. If no such an element is found, return end().
• lower_bound() returns an iterator pointing to the first element in the range [first, last) which is greater or equal to the value. If no such an element is found, return end().

Quick summary

• upper bound return first element which is > value. If not, return end().
• lower bound return first element which is ≥ value. If not, return end().

Examples

#include <bits/stdc++.h> 
int main() 
{ 
    std::vector<int> v{ 10, 20, 30, 30, 50 }; 
  
    // Print vector 
    std::cout << "Vector contains :"; 
    for (unsigned int i = 0; i < v.size(); i++) 
        std::cout << " " << v[i]; 
    std::cout << "\n"; 
  
    std::vector<int>::iterator low, upp; 
 
    std::cout<<"******* lower_bound *********"<<std::endl;
    low = std::lower_bound(v.begin(), v.end(), 20); 
    std::cout << "\nlower_bound for element 20 at position : " << (low - v.begin()); 
    low = std::lower_bound(v.begin(), v.end(), 25); 
    std::cout << "\nlower_bound for element 25 at position : " << (low - v.begin())<<std::endl; 
    
    
    std::cout<<"****** upper_bound ************"<<std::endl;
    upp =…