C++ Algorithm is_partitioned()用法及代码示例

C++ 算法 is_partitioned() 用于测试范围 [first, last) 是否根据谓词进行分区。换句话说，范围内满足谓词的所有元素都在序列的开头。

如果范围为空，则返回 true。

用法

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

参数

first:指向范围内第一个元素的输入迭代器。

last:一个输入迭代器，指向范围中过去的最后一个元素。

pred: 一个用户定义的一元谓词函数，它为预期在范围开头找到的元素返回真。

返回值

如果范围为空或由给定的谓词 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 [first, last) 中的对象。

每个元素只被访问一次。

异常

如果 pred 或迭代器上的操作引发异常，则此函数将引发异常。

请注意，无效参数会导致未定义的行为。

例子1

让我们看一个简单的例子来演示 is_partitioned() 的使用：

#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

例子2

让我们看另一个简单的例子：

#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.

例子3

让我们看另一个简单的例子：

#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例子：

#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.

相关用法

注：本文由纯净天空筛选整理自 C++ Algorithm is_partitioned()。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。