C++ 算法 is_partitioned()函数

C++ 算法 is_partitioned() 用于根据谓词测试指定的范围 [first, last) 是否已被分隔。换句话说，范围内满足谓词的所有元素位于序列的开头。

如果范围为空，则返回 true。

语法

template <class InputIterator, class UnaryPredicate>
  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 ：指向范围末尾后一个元素的输入迭代器。

pred ：用户定义的一元谓词函数，对于在范围开头预期出现的元素返回true。

返回值

如果范围为空或由给定的谓词pred分隔，则此函数返回true，否则返回false。

复杂度

复杂度与范围[first，last)线性相关：对于每个元素调用pred，直到发现不匹配。

数据竞争

访问范围[first，last)中的对象。

每个元素仅被访问一次。

异常

如果pred或迭代器上的操作引发异常，则此函数会引发异常。

请注意，无效的参数会导致未定义的行为。

示例1

我们来看一个简单的示例，演示is_partitioned()的用法：

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
  vector<int> 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?"<<endl;
  // Is it divided into an even group and an odd group?  
  if (is_partitioned(v.begin(), v.end(), pred)) {
    cout << "Yes,It is Partitioned" << endl;
  }
  else {
    cout << "No,It is not Partitioned" << endl;
  }

  return 0;
}

输出：

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

Is it partitioned?
Yes,It is Partitioned

示例2

让我们看另一个简单的示例：

#include <iostream> 
#include <algorithm> 
#include <vector> 

// Defining the BinaryFunction 
bool pred(int a) 
{ 
    return (a % 2 == 0); 
} 

using namespace std; 
int main() 
{ 
    // Declaring first vector 
    vector<int> 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.

示例3

让我们看另一个简单的示例：

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

int main()
{
    std::array<int, 9> 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 

示例4

让我们看另一个简单的示例：

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
  vector<int> 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?"<<endl;
  // Is it divided into an even group and an odd group?  
  if (is_partitioned(v.begin(), v.end(), pred)) {
    cout << "Yes, It is Partitioned." << endl;
  }
  else {
    cout << "No, It is not Partitioned." << endl;
  }

  return 0;
}

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.