C++ 头文件algorithm 1——partition

函数 功能 partition 将元素划分为两个集合 is_partitioned 测试集合是否被划分 stable_partition 将元素划分为两个集合，保持元素的相对顺序 partition_copy 将元素划分为两个集合 partition_point 获取划分点

partition

ForwardIterator partition (ForwardIterator first, ForwardIterator last, UnaryPredicate pred);

first,last表示元素范围[first,last);
pred:表示分组条件，它是一个一元函数，也可以是函数指针或函数对象。
返回值是一个迭代器，指向第二个元素组的第一个元素；如果这个组是空的，则是最后一个元素。

example

#include<iostream>#include<algorithm>#include<vector>using namespace std;bool isOdd(int i){ return (i % 2) == 1; }int main(){    vector<int> myvector;    for (int i = 1; i < 10; ++i) myvector.push_back(i);    vector<int>::iterator bound;    bound = partition(myvector.begin(), myvector.end(), isOdd);    cout << "odd element:";    for (vector<int>::iterator it = myvector.begin(); it != bound; ++it)        cout << " " << *it;    cout << "\n";    cout << "even element:";    for (vector<int>::iterator it = bound; it != myvector.end(); ++it)        cout << " " << *it;    cout << "\n";    return 0;}

output

is_partitioned

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

first,last表示元素范围[first,last);
pred: 一元函数接受集合内的一个元素作为参数，并返回一个bool值。返回的值表示元素是否属于第一个组（如果是true，则该元素将在返回false的所有元素之前）。函数不会改变参数值，它也可以是函数指针或函数对象。
若范围[first,last)内所有元素满足pred，返回true;若元素集合为空，也返回true。

example

#include<iostream>#include<algorithm>#include<array>using namespace std;bool isOdd(int i){ return (i % 2) == 1; }int main(){    array<int, 7> test={1,2,3,4,5,6,7};    //print out    for (int& x : test)        cout << x << " ";    if (is_partitioned(test.begin(), test.end(), isOdd))        cout << "partitioned\n";    else        cout << "no partitioned\n";    //partition    partition(test.begin(), test.end(), isOdd);    //print out again    for (int& x : test)        cout << x << " ";    if (is_partitioned(test.begin(), test.end(), isOdd))        cout << "partitioned\n";    else        cout << "no partitioned\n";}

output

stable_partition

BidirectionalIterator stable_partition (BidirectionalIterator first,
BidirectionalIterator last,
UnaryPredicate pred);

stable_partition 与partition不同，每个组中元素的相对顺序是保留的。参数first，last，pred同partition。

example

#include<iostream>#include<algorithm>#include<vector>using namespace std;bool isOdd(int i){ return (i % 2) == 1; }int main(){    vector<int> myvector;    for (int i = 1; i < 10; ++i) myvector.push_back(i);    vector<int>::iterator bound;    bound = stable_partition(myvector.begin(), myvector.end(), isOdd);    cout << "odd element:";    for (vector<int>::iterator it = myvector.begin(); it != bound; ++it)        cout << " " << *it;    cout << "\n";    cout << "even element:";    for (vector<int>::iterator it = bound; it != myvector.end(); ++it)        cout << " " << *it;    cout << "\n";    return 0;}

output

partition_copy

partition_copy (InputIterator first, InputIterator last, OutputIterator1 result_true, OutputIterator2 result_false, UnaryPredicate pred)

First, last表示范围[first,last);Result_true:输出迭代器到该范围的初始位置，在该范围中存储pred返回true的元素;Result_false：输出迭代器到该范围的初始位置，在该范围中存储pred返回false的元素;Pred:同partition，stable_partition。

example

#include<iostream>#include<algorithm>#include<vector>using namespace std;bool isOdd(int i){ return (i % 2) == 1; }int main(){    vector<int> test = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };    vector<int> odd, even;    //resize vectors to proper size    unsigned n = count_if(test.begin(), test.end(), isOdd);    odd.resize(n);    even.resize(test.size()-n);    //partition    partition_copy(test.begin(), test.end(), odd.begin(), even.begin(), isOdd);    cout << "odd:";    for (int& x : odd)        cout << " " << x;    cout << "\n";    cout << "even";    for (int& x : even)        cout << " " << x;    cout << "\n";    return 0;}

output

partition_point

ForwardIterator partition_point (ForwardIterator first, ForwardIterator last, UnaryPredicate pred)
返回值是迭代器，它指向在[first.last)内第一个pred不为true的元素；如果对任何元素都不正确，则指向最后一个元素。

example

#include<iostream>#include<algorithm>#include<vector>using namespace std;bool isOdd(int i){ return (i % 2) == 1; }int main(){    vector<int> test = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };    vector<int> odd;    stable_partition(test.begin(), test.end(), isOdd);    auto it = partition_point(test.begin(), test.end(), isOdd);    odd.assign(test.begin(), it);    //print odd    cout << "odd:";    for (int& x : odd)        cout << " " << x;    cout << "\n";    return 0;}

output