upper_bound and lower_bound for non increasing vector in c++

The lower_bound() and upper_bound() functions by default work on non decreasing array. The lower_bound() function finds iterator of first element that does not compare less to given element. The upper_bound() function returns iterator to first element that is greater.

Given an array converting this to an non increasing vector, applying the std:: upper_bound and std:: lower_bound function to the vector

For array sorted in non-increasing array, lowe_bound() finds iterator to first element that does not compare greater than to given element. upper_bound() finds iterator to first element that is smaller than given element. We use grater() for this purpose.

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// CPP program to demonstrate working of lower_bound()
// and upper_bound() for array sorted in non-decreasing
// array,
#include <algorithm>
#include <iostream>
#include <vector>
  
int main()
{
    int unsorted[10] = { 3, 3, 2, 1, 5, 5, 4, 3, 7, 8 };
    std::vector<int> v(unsorted, unsorted + 10);
  
    // sorting vector in non increasing order. Vector
    // becomes {8, 7, 5, 5, 4, 3, 3, 3, 2, 1}
    std::sort(v.begin(), v.end(), std::greater<int>());
  
    std::vector<int>::iterator low, up;
    low = std::lower_bound(v.begin(), v.end(), 3, std::greater<int>());         
    up = std::upper_bound(v.begin(), v.end(), 5, std::greater<int>());          
  
    std::cout << "lower_bound at position " << (low - v.begin()) << '\n';
    std::cout << "upper_bound at position " << (up - v.begin()) << '\n';
  
    return 0;
}

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Output:

lower_bound at position 5
upper_bound at position 4


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