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chinesedragon
的主页网址:http://wonyen.net/home.aspx?id=chinesedragon
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| § chinesedragon
的【理论研究】专栏
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| 作者：chinesedragon 发表时间：
2005/12/3 13:33:09 查看：
4988
评论：
2
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| 标题：
素数缓冲求法，可重用类
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素数缓冲求法，可重用类
#include <iostream>
#include <algorithm>
#include <vector>
#include <iterator>
template <typename T>
class PrimerCache
- {
typedef T ValueType;
typedef std::vector<ValueType> IntArray;
typedef typename IntArray::const_iterator IntPtr;
static IntArray mCache;
protected:
bool Test(ValueType num) const
- {
// make sure : half < mCache.back()
// !!! IncreaseCache(half) promised this !!!
ValueType half = num / 2 + 1;
for(IntPtr i = mCache.begin(); *i < half && i != mCache.end(); ++i)
- {
if( num % (*i) == 0)
- {
return false;
}
}
return true;
}
void IncreaseCache(ValueType num) const
- {
ValueType upper = mCache.back();
while (upper < num)
- {
upper++;
if( Test(upper))
- {
mCache.push_back(upper);
}
}
}
bool InCache(ValueType num) const
- {
return std::binary_search(mCache.begin(), mCache.end(), num);
}
public:
PrimerCache(ValueType lowerNum = 1000)
- {
IsPrimer(lowerNum);
}
bool IsPrimer(ValueType num) const
- {
ValueType biggestPrimer = mCache.back() + 1;
if( biggestPrimer > num)
- {
return InCache(num);
}
else
- {
IncreaseCache(num);
return Test(num);
}
}
friend std::ostream& operator<<(std::ostream& out, PrimerCache const& primerCache)
- {
IntArray& cache = primerCache.mCache;
out << "Primer Cache Has " << cache.size() << " elements, they are " << std::endl;
std::copy(cache.begin(), cache.end(), std::ostream_iterator<int>(out, ","));
return out;
}
};
//the one and only cache;
template <typename T>
typename PrimerCache<T>::IntArray PrimerCache<T>::mCache = IntArray(1, 2);
template <typename CacheType>
void TestPrimer(CacheType& cache, int num)
- {
int test = num;
std::cout<< test << " is primer? "<< std::boolalpha << cache.IsPrimer(test) << std::endl;
}
int main()
- {
PrimerCache<int> primer;
int test;
TestPrimer(primer, 1);
TestPrimer(primer, 2);
TestPrimer(primer, 4);
TestPrimer(primer, 5);
TestPrimer(primer, 99);
TestPrimer(primer, 97);
TestPrimer(primer, 101);
TestPrimer(primer, 102);
TestPrimer(primer, 98);
TestPrimer(primer, 96);
std::cout << primer << std::endl;
std::cout << "primer is " << sizeof ( PrimerCache<int>) << std::endl;
PrimerCache<short> p(10);
TestPrimer(p, 1);
TestPrimer(p, 2);
std::cout << p << std::endl;
return 0;
}
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回复者：王博 回复时间：2012/7/24 22:17:03 [第1评]
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