C++ 算法 中的 partition_point函数

template <class ForwardIterator, class UnaryPredicate>
ForwardIterator partition_point (ForwardIterator first, ForwardIterator last,
                                   UnaryPredicate pred);

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

using namespace std;
 
int main()
{
    array<int, 9> v = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
 
    auto is_even = [](int i)
        { return i % 2 == 0; };
    partition(v.begin(), v.end(), is_even);
 
    auto p = std::partition_point(v.begin(), v.end(), is_even);
 
    cout << "Before partition:\n    ";
    copy(v.begin(), p, ostream_iterator<int>(cout, " "));
    cout << "\nAfter partition:\n    ";
    copy(p, v.end(), ostream_iterator<int>(cout, " "));
    
    return 0;
}

#include <iostream>    //std::cout
#include <algorithm>   //std::partition, std::partition_point
#include <vector>      //std::vector

using namespace std;

bool IsOdd (int i) { return (i%2)==1; }

int main () {
  vector<int> foo {1,2,3,4,5,6,7,8,9};
  vector<int> odd;

  partition (foo.begin(),foo.end(),IsOdd);

  auto it = partition_point(foo.begin(),foo.end(),IsOdd);
  odd.assign (foo.begin(),it);

 //print contents of odd:
  cout << "odd:";
  for (int& x:odd) cout << ' ' << x;
  cout << '\n';

  return 0;
}

#include<iostream> 
#include<algorithm>//for partition algorithm 
#include<vector>//for vector 
using namespace std; 
int main() 
{ 
   //Initializing vector 
    vector<int> vect = { 2, 1, 5, 6, 8, 7 }; 
      
   //partitioning vector using stable_partition() 
   //in sorted order 
    stable_partition(vect.begin(), vect.end(), [](int x) 
    { 
        return x%2 == 0;         
    }); 
      
   //Displaying partitioned Vector 
    cout << "The partitioned vector is : "; 
    for (int &x : vect) cout << x << " "; 
    cout << endl; 
      
   //Declaring iterator 
    vector<int>::iterator it1; 
      
   //using partition_point() to get ending position of partition 
    auto it = partition_point(vect.begin(), vect.end(), [](int x) 
    { 
        return x%2==0; 
    }); 
      
   //Displaying partitioned Vector 
    cout << "The vector elements returning true for condition are : "; 
    for ( it1= vect.begin(); it1!=it; it1++) 
    cout << *it1 << " "; 
    cout << endl; 
      
    return 0; 
      
} 

#include <iostream>//std::cout 
#include <algorithm>//std::partition, std::partition_point 
#include <vector>//std::vector 

using namespace std;
  
bool IsNegative(int i) { return (i < 0); } 
  
int main() 
{ 
    vector<int> data{ 1, -1, 3, -4, 5, 2, -2, 4, -5, -3 }; 
    vector<int> negative, positive; 
  
   //partition data on the basis of odd elements using  
   //pred IsNegative() 
    stable_partition(data.begin(), data.end(), IsNegative); 
  
   //gets the partition point based on odd elements 
    auto it = partition_point(data.begin(), data.end(),  IsNegative); 
  
   //assign elements to odd from beginning till 
   //partition point. 
    negative.assign(data.begin(), it); 
    positive.assign(it, data.end()); 
  
   //print contents of odd: 
    cout << "Negative: "; 
    for (int& x : negative) 
        cout << ' ' << x; 
    cout << '\n'; 
  
   //print contents of even: 
    cout << "Positive: "; 
    for (int& x : positive) 
        cout << ' ' << x; 
    cout << '\n'; 
  
    return 0; 
}