Espaços nominais
Variantes
Acções

std::count, std::count_if

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< cpp‎ | algorithm

 
 
Biblioteca algoritmo
Funções
Original:
Functions
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Não modificar operações de seqüência
Original:
Non-modifying sequence operations
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all_of
any_of
none_of
(C++11)
(C++11)
(C++11)
for_each
count
count_if
mismatch
equal
Modificando operações de seqüência
Original:
Modifying sequence operations
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Particionamento operações
Original:
Partitioning operations
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Operações de classificação (em intervalos ordenados)
Original:
Sorting operations (on sorted ranges)
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Binários operações de busca (em intervalos ordenados)
Original:
Binary search operations (on sorted ranges)
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Definir operações (em intervalos ordenados)
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Set operations (on sorted ranges)
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Operações de pilha
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Heap operations
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Mínimo / máximo de operações
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Minimum/maximum operations
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Operações numéricas
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Numeric operations
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C biblioteca
Original:
C library
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Definido no cabeçalho <algorithm>
template< class InputIt, class T >

typename iterator_traits<InputIt>::difference_type

    count( InputIt first, InputIt last, const T &value );
(1)
template< class InputIt, class UnaryPredicate >

typename iterator_traits<InputIt>::difference_type

    count_if( InputIt first, InputIt last, UnaryPredicate p );
(2)
Retorna o número de elementos no intervalo [first, last) satisfazer critérios específicos. A primeira versão conta os elementos que são iguais para value, a segunda versão conta com elementos para os quais predicado p retornos true.
Original:
Returns the number of elements in the range [first, last) satisfying specific criteria. The first version counts the elements that are equal to value, the second version counts elements for which predicate p returns true.
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Índice

[editar] Parâmetros

first, last -
a gama de elementos para examinar
Original:
the range of elements to examine
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value -
o valor a ser procurado
Original:
the value to search for
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p - unary predicate which returns ​true
para os elementos necessários
Original:
for the required elements
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.

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

 bool pred(const Type &a);

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

Type requirements
-
InputIt must meet the requirements of InputIterator.

[editar] Valor de retorno

número de elementos que satisfaz a condição.
Original:
number of elements satisfying the condition.
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[editar] Complexidade

exatamente last - first comparações / aplicações do predicado
Original:
exactly last - first comparisons / applications of the predicate
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[editar] Possível implementação

First version
template<class InputIt, class T>
typename iterator_traits<InputIt>::difference_type
    count(InputIt first, InputIt last, const T& value)
{
    typename iterator_traits<InputIt>::difference_type ret = 0;
    for (; first != last; ++first) {
        if (*first == value) {
            ret++;
        }
    }
    return ret;
}
Second version
template<class InputIt, class UnaryPredicate>
typename iterator_traits<InputIt>::difference_type
    count_if(InputIt first, InputIt last, UnaryPredicate p)
{
    typename iterator_traits<InputIt>::difference_type ret = 0;
    for (; first != last; ++first) {
        if (p(*first)) {
            ret++;
        }
    }
    return ret;
}

[editar] Exemplo

O código a seguir usa count para determinar quantos números inteiros em uma std::vector corresponder a um valor alvo .
Original:
The following code uses count to determine how many integers in a std::vector match a target value.
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#include <algorithm>
#include <iostream>
#include <vector>
 
int main()
{
    int data[] = { 1, 2, 3, 4, 4, 3, 7, 8, 9, 10 };
    std::vector<int> v(data, data+10);
 
    int target1 = 3;
    int target2 = 5;
    int num_items1 = std::count(v.begin(), v.end(), target1);
    int num_items2 = std::count(v.begin(), v.end(), target2);
 
    std::cout << "number: " << target1 << " count: " << num_items1 << '\n';
    std::cout << "number: " << target2 << " count: " << num_items2 << '\n';
}

Saída:

number: 3 count: 2
number: 5 count: 0

Este exemplo usa um lambda expressão contar elementos divisível por 3 .
Original:
This example uses a lambda expressão to count elements divisible by 3.
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#include <algorithm>
#include <iostream>
#include <vector>
 
int main()
{
    int data[] = { 1, 2, 3, 4, 4, 3, 7, 8, 9, 10 };
    std::vector<int> v(data, data+10);
 
    int num_items1 = std::count_if(v.begin(), v.end(), [](int i) {return i % 3 == 0;});
 
    std::cout << "number divisible by three: " << num_items1 << '\n';
}

Saída:

number divisible by three: 3