我一直在玩C ++ 11功能,以便像python的itertools.combinations(输入,2)一样,到目前为止这就是我所拥有的:
编辑按照@DavidRodríguez-dribeas的建议删除了外部lambda
#include <iostream>
#include <functional>
#include <vector>
using namespace std;
template <class T>
function<pair<T*, T*>()> combinations(vector<T> & input) {
auto it1 = input.begin();
auto end = input.end();
auto it2 = next(it1);
return [=]() mutable {
if (it2 == end) {
it1++;
it2 = next(it1);
}
if (it2 != end)
return pair<T*,T*>(&(*it1), &(*it2++));
return pair<T*,T*>(&*end, &*end);
};
};
int main (void) {
vector<int> numbers{1,2,3,4,5,6};
auto func = combinations(numbers);
while ( true ) {
auto i = func();
if (i.first == &*(numbers.end())) break;
cout << *(i.first) << ',' << *(i.second) << endl;
}
return 0;
};
我不满意用于迭代组合的任何建议清理它的方法吗?
答案 0 :(得分:1)
Here是我最喜欢的方式的文档和代码。以下是该库如何用于您的示例:
#include <iostream>
#include <vector>
#include "combinations"
using namespace std;
int main (void) {
vector<int> numbers{1,2,3,4,5,6};
for_each_combination(numbers.begin(), numbers.begin()+2, numbers.end(),
[](vector<int>::const_iterator b, vector<int>::const_iterator e)
{
if (b != e)
{
cout << *b;
for (auto i = b+1; i != e; ++i)
cout << ',' << *i;
cout << endl;
}
return false;
});
}
1,2
1,3
1,4
1,5
1,6
2,3
2,4
2,5
2,6
3,4
3,5
3,6
4,5
4,6
5,6
如果需要出现,将示例用法改为考虑3个或4个项目而不是2个是微不足道的。一个也可以同时处理N个中的各种排列。
<强>更新强>
添加一个间接级别来说明如何处理在向量中移动/交换时效率不高的项目向量:
#include <iostream>
#include <vector>
#include "combinations"
using namespace std;
int main (void) {
vector<int> numbers{1,2,3,4,5,6};
vector<vector<int>::const_iterator> num_iters;
num_iters.reserve(numbers.size());
for (auto i = numbers.begin(); i != numbers.end(); ++i)
num_iters.push_back(i);
for_each_combination(num_iters.begin(), num_iters.begin()+2, num_iters.end(),
[](vector<vector<int>::const_iterator>::const_iterator b,
vector<vector<int>::const_iterator>::const_iterator e)
{
if (b != e)
{
cout << **b;
for (auto i = b+1; i != e; ++i)
cout << ',' << **i;
cout << endl;
}
return false;
});
}
答案 1 :(得分:1)
我发现Oliver Kowalke的coroutine库已经被Boosts同行评审所接受,并且应该包含在下一个版本中。通过使用boost-dev repo(https://gitorious.org/boost-dev/boost-dev)的协程分支,我稍稍跳了一下枪。
g++ -I path/to/boost-dev -std=c++11 test_code.cpp -o run_test_code -static -L path/to/boost-dev/stage/lib/ -lboost_context
#include <boost/coroutine/all.hpp>
#include <boost/bind.hpp>
#include <boost/range.hpp>
#include <iostream>
#include <vector>
using namespace std;
using namespace boost;
template <typename T>
using coro_pairT_void = coroutines::coroutine<pair<T&,T&>(void)>;
template <typename T>
void combinations(typename coro_pairT_void<T>::caller_type & self, vector<T> & input ) {
for (auto it1 = input.begin(), itend = input.end(); it1 != itend; it1++) {
for (auto it2 = std::next(it1); it2 != itend; it2++) {
self(pair<T&, T&>(*it1,*it2));
}
}
};
int main( void ) {
vector<int> numbers{1,2,3,4,5,6};
coro_pairT_void<int> func(bind(combinations<int>, _1, numbers));
for (auto it(begin(func)), itend(end(func)); it != itend; ++it) {
cout << it->first << ',' << it->second << endl;
}
return 0;
};