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std::lower_bound

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< cpp‎ | algorithm

 
 
Biblioteca de algoritmos
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(C++17)
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Operaciones de búsqueda binaria
lower_bound
Operaciones de set (en rangos ordenados)
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Bibliotecas C
 
Definido en la cabecera <algorithm>
template< class ForwardIt, class T >
ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value );
(1)
template< class ForwardIt, class T, class Compare >
ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value, Compare comp );
(2)

Returns an iterator pointing to the first element in the range [first, last) that is not less than value. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.

Contenido

[editar] Parámetros

first, last - iterators defining the range to examine
value -
valor para comparar los elementos a
Original:
value to compare the elements to
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comp - comparison function which returns ​true if the first argument is less than the second.

The signature of the comparison function should be equivalent to the following:

 bool cmp(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The type Type1 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to Type1. The type Type2 must be such that an object of type T can be implicitly converted to Type2. ​

Requerimientos de tipo
-
ForwardIt debe reunir los requerimientos de ForwardIterator.

[editar] Valor de retorno

Iterator pointing to the first element that is not less than value, or last if no such element is found.

[editar] Complejidad

Logarítmica en la distancia entre first y last
Original:
Logarithmic in the distance between first and last
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[editar] Posible implementación

Primera versión
template<class ForwardIt, class T>
ForwardIt lower_bound(ForwardIt first, ForwardIt last, const T& value)
{
    ForwardIt it;
    std::iterator_traits<ForwardIt>::difference_type count, step;
    count = std::distance(first, last);
 
    while (count > 0) {
        it = first; 
        step = count / 2; 
        std::advance(it, step);
        if (*it < value) {
            first = ++it; 
            count -= step + 1; 
        } else count = step;
    }
    return first;
}
Segunda versión
template<class ForwardIt, class T, class Compare>
ForwardIt lower_bound(ForwardIt first, ForwardIt last, const T& value, Compare comp)
{
    ForwardIt it;
    std::iterator_traits<ForwardIt>::difference_type count, step;
    count = std::distance(first,last);
 
    while (count > 0) {
        it = first;
        step = count / 2;
        std::advance(it, step);
        if (comp(*it, value)),
            first = ++it;
            count -= step + 1;
        } else count = step;
    }
    return first;
}

[editar] Ejemplo

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
 
int main()
{
    std::vector<int> data = { 1, 1, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 6 };
 
    auto lower = std::lower_bound(data.begin(), data.end(), 4);
    auto upper = std::upper_bound(data.begin(), data.end(), 4);
 
    std::copy(lower, upper, std::ostream_iterator<int>(std::cout, " "));
}

Salida:

4 4 4

[editar] Ver también

El rendimiento es de los elementos que coinciden con una clave específica
Original:
returns range of elements matching a specific key
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(plantilla de función) [editar]
devuelve un iterador al primer elemento' mayor que un cierto valor
Original:
returns an iterator to the first element greater than a certain value
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(plantilla de función) [editar]