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📜  C++ STL-algorithm.is_partitioned()函数

📅  最后修改于: 2020-10-17 04:25:16             🧑  作者: Mango

C++ STL algorithmis_partitioned()

C++ STL algorithm.is_partitioned()用于测试是否根据谓词对范围[first，last)进行了分区。换句话说，满足谓词范围内的所有元素都在序列的开头。

如果范围为空，则返回true。

句法

template 
  bool is_partitioned (InputIterator first, InputIterator last, UnaryPredicate pred);

参数

first：指向范围中第一个元素的输入迭代器。

last：指向范围中最后一个元素的输入迭代器。

pred：用户定义的一元谓词函数，对于预期在范围开头找到的元素，该函数返回true。

返回值

如果范围为空或被给定的谓词pred分区，则此函数返回true，否则返回false。

复杂度

复杂度在[first，last)范围内是线性的：为每个元素调用pred直到发现不匹配。

数据竞争

访问范围为[first，last)的对象。

每个元素仅被访问一次。

异常处理

如果pred或迭代器上的操作引发异常，则此函数引发异常。

请注意，无效的参数会导致未定义的行为。

例子1

让我们看一个简单的示例来演示is_partitioned()的用法：

#include 
#include 
#include 

using namespace std;

int main()
{
  vector v = {1, 2, 3, 4, 5};
  
  cout<<"Before Partition: ";
    for_each(v.begin(), v.end(), [](int v) {
   cout << v << " ";
  });


  auto pred = [](int x) { return x % 2 == 0; };

  // Divide it into an even group and an odd group 
  partition(v.begin(), v.end(), pred);
  cout<<"\nAfter partition : ";
  for_each(v.begin(), v.end(), [](int x) {
   cout << x << " ";
  });

  cout<<"\n\nIs it partitioned?"<

输出：

Before Partition: 1 2 3 4 5 
After partition : 4 2 3 1 5 

Is it partitioned?
Yes,It is Partitioned

例子2

让我们看另一个简单的例子：

#include  
#include  
#include  
  
// Defining the BinaryFunction 
bool pred(int a) 
{ 
    return (a % 2 == 0); 
} 
  
using namespace std; 
int main() 
{ 
    // Declaring first vector 
    vector v1 = { 2, 4, 6, 3, 5, 7, 9 }; 
  
    // Using std::is_partitioned 
    bool b = std::is_partitioned(v1.begin(), v1.end(), pred); 
  
    if (b == 1) { 
        cout << "All the even no. are present before odd no."; 
    } else { 
        cout << "All the even no. are not present before odd no."; 
    } 
  
    // Inserting an even no. at the end of v1 
    // so std::is_partitioned returns false 
    v1.push_back(16); 
  
    // Now again using std::is_partitioned 
    b = std::is_partitioned(v1.begin(), v1.end(), pred); 
  
    if (b == 1) { 
        cout << "\nAll the even no. are present before odd no."; 
    } else { 
        cout << "\nAll the even no. are not present before odd no."; 
    } 
  
    return 0; 
}

输出：

All the even no. are present before odd no.
All the even no. are not present before odd no.

例子3

让我们看另一个简单的例子：

#include 
#include 
#include 
 
int main()
{
    std::array v = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
 
    auto is_even = [](int i){ return i % 2 == 0; };
    std::cout.setf(std::ios_base::boolalpha);
    std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
 
    std::partition(v.begin(), v.end(), is_even);
    std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
 
    std::reverse(v.begin(), v.end());
    std::cout << std::is_partitioned(v.begin(), v.end(), is_even);
}

输出：

false true false

例子4

让我们看另一个简单的例子：

#include 
#include 
#include 

using namespace std;

int main()
{
  vector v = {11, 2, 3, 4, 15, 12};
  
  cout<<"Before Partition: ";
    for_each(v.begin(), v.end(), [](int v) {
   cout << v << " ";
  });


  auto pred = [](int x) { return x < 10; };
 
  // Divide it into an even group and an odd group 
  partition(v.begin(), v.end(), pred);
  cout<<"\nAfter partition: ";
  for_each(v.begin(), v.end(), [](int x) {
   cout << x << " ";
  });

  cout<<"\n\nIs it partitioned?"<

输出：

Before Partition: 11 2 3 4 15 12 
After partition: 4 2 3 11 15 12 

Is it partitioned?
Yes, It is Partitioned.