CODEWITHSUNDEEP
c++arraysfunctionsorting
racoot
racoot

Reputation: 43

Is there a function like lower_bound that returns the last value instead of the first?

For example, if I have a sorted array 

{1,1,1,1,1,4,5}

and I want to know the rightmost index of 1, is there a function that will allow me to do that? (Apart from reverse sorting the array)

Upvotes: 3

Views: 174

Answers (3)

Ripi2
Ripi2

Reputation: 7198

#include <iostream>
#include <array>
#include <algorithm>
#include <iterator>

int main()
{
    std::array<int, 6> data({2,2,2,2,4,7});

    auto it = std::upper_bound(data.begin(), data.end(), 2);
    int index = std::distance(data.begin(), it) - 1;

    std::cout << "index for last '2' is " << index << std::endl;
}

output:
index for last '2' is 3

Upvotes: 1

Slava
Slava

Reputation: 44258

This should work:

auto p = std::equal_range( std::begin(v), std::end(v), 1 );
if( p.first != p.second ) {
    auto it = p.second - 1;
    //...
}

live example

Upvotes: 4

bipll
bipll

Reputation: 11940

There's none so you should craft one on your own.

template<class Ctr, class Elem> auto rightmost(Ctr &&c, Elem &&e) {
    using std::begin;
    using std::end;
    auto b{begin(c)};
    auto retVal{std::upper_bound(b, end(c), e)};
    return retVal == b? b : --retVal;
}

Upvotes: 1

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