C++在其STL算法库中有一个类，该类允许我们使用某些内置函数轻松进行分区算法。分区是指根据给定条件划分容器元素的动作。
分区操作 ：
1. partition(beg，end，condition)：-此函数用于根据其参数中提到的条件对元素进行分区。
2. is_partitioned(beg，end，condition)：-如果容器已分区，则此函数返回布尔值true，否则返回false。
// C++ code to demonstrate the working of
// partition() and is_partitioned()
#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 };
// Checking if vector is partitioned
// using is_partitioned()
is_partitioned(vect.begin(), vect.end(), [](int x)
{
return x%2==0;
})?
cout << "Vector is partitioned":
cout << "Vector is not partitioned";
cout << endl;
// partitioning vector using partition()
partition(vect.begin(), vect.end(), [](int x)
{
return x%2==0;
});
// Checking if vector is partitioned
// using is_partitioned()
is_partitioned(vect.begin(), vect.end(), [](int x)
{
return x%2==0;
})?
cout << "Now, vector is partitioned after partition operation":
cout << "Vector is still not partitioned after partition operation";
cout << endl;
// Displaying partitioned Vector
cout << "The partitioned vector is:";
for (int &x:vect) cout << x << " ";
return 0;
}输出：
Vector is not partitioned Now, vector is partitioned after partition operation The partitioned vector is:2 8 6 5 1 7
在上面的代码中，分区函数根据元素是偶数还是奇数对向量进行分区，偶数元素从奇数元素开始的划分没有特定顺序。
3. stable_partition(beg，end，condition)：-此函数用于根据其自变量中提到的条件对元素进行分区，从而保留元素的相对顺序。
4. partition_point(beg，end，condition)：-此函数返回一个迭代器，该迭代器指向容器的分区点，即条件不成立的分区范围[beg，end)中的第一个元素。容器应该已经分区了，此函数才能起作用。
// C++ code to demonstrate the working of
// stable_partition() and partition_point()
#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;
}输出：
The partitioned vector is:2 6 8 1 5 7 The vector elements returning true for condition are:2 6 8
在上面的代码中，偶数和奇数元素按升序进行了划分(排序)
5. partition_copy(beg，end，beg1，beg2, condition)：-此函数在其参数中提到的differnet容器中复制分区的元素。它需要5个参数。容器的开始和结束位置，必须复制元素的新容器的开始位置(元素返回条件为true)，必须复制其他元素的新容器的开始位置(元素返回条件为false)和条件。调整新容器的大小对于此函数是必需的。
// C++ code to demonstrate the working of
// partition_copy()
#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 };
// Declaring vector1
vector<int> vect1;
// Declaring vector1
vector<int> vect2;
// Resizing vectors to suitable size using count_if() and resize()
int n = count_if (vect.begin(), vect.end(), [](int x)
{
return x%2==0;
} );
vect1.resize(n);
vect2.resize(vect.size()-n);
// Using partition_copy() to copy partitions
partition_copy(vect.begin(), vect.end(), vect1.begin(),
vect2.begin(), [](int x)
{
return x%2==0;
});
// Displaying partitioned Vector
cout << "The elements that return true for condition are:";
for (int &x:vect1)
cout << x << " ";
cout << endl;
// Displaying partitioned Vector
cout << "The elements that return false for condition are:";
for (int &x:vect2)
cout << x << " ";
cout << endl;
return 0;
}输出：
The elements that return true for condition are:2 6 8 The elements that return false for condition are:1 5 7
相关用法
注：本文由纯净天空筛选整理自 std::partition in C++ STL。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。