Type Traits 实例，提高效率 (转)

最新推荐文章于 2025-11-01 09:04:16 发布

转载最新推荐文章于 2025-11-01 09:04:16 发布 · 90 阅读

本文介绍了一个使用TypeTraits来区分简单比较与复杂比较的C++模板实现案例，其中包括了二分查找与下界查找算法的具体实现。通过定义不同的比较特质类，实现了根据不同类型的比较需求选择最合适的算法。

Type Traits 实例，提高效率 (转)[@more@]

#include "iostream"
using namespace std;

class SimpleCompareTrait { };
class ComplexCompareTrait { };

template class ComplexCompare
{
public:
typedef T ValueType;
typedef ComplexCompareTrait CompareTrait;
};

template class SimpleCompare
{
public:
typedef T ValueType;
typedef SimpleCompareTrait CompareTrait;
};

template
Iterator __LowerBound(Iterator first, Iterator last, T val,
Compare comp, ComplexCompareTrait)
{
size_t len = 0;
size_t half;
Iterator middle;

len = last - first;
while (len > 0)
{
half = len >> 1;
middle = first;
middle += half;
if (comp(*middle, val) < 0)
{
first = middle;
++first;
len = len - half - 1;
} else
len = half;
}
return first;
}

template
Iterator __LowerBound(Iterator first, Iterator last, T val,
Compare comp, SimpleCompareTrait)
{
size_t len = 0;
size_t half;
Iterator middle;

len = last - first;
while (len > 0)
{
half = len >> 1;
middle = first;
middle += half;
if (comp(*middle, val))
{
first = middle;
++first;
len = len - half - 1;
} else
len = half;
}
return first;
}

template
Iterator LowerBound(Iterator first, Iterator last, T val, Compare comp)
{
return __LowerBound(first, last, val, comp, Compare::CompareTrait());
}

template
Iterator __BinSearch(Iterator first, Iterator last, T val,
Compare comp, ComplexCompareTrait)
{
size_t len = 0;
size_t half;
Iterator middle;

len = last - first;
while (len > 0)
{
half = len >> 1;
middle = first;
middle += half;
int iComp = comp(*middle, val);
if (iComp < 0)
{
first = middle;
++first;
len = len - half - 1;
}
else if (iComp > 0)
{
len = half;
} else
return middle;
}
return last;
}

template
Iterator __BinSearch(Iterator first, Iterator last, T val,
Compare comp, SimpleCompareTrait)
{
size_t len = 0;
size_t half;
Iterator middle;

len = last - first;
while (len > 0)
{
half = len >> 1;
middle = first;
middle += half;
if (comp(*middle, val))
{
first = middle;
++first;
len = len - half - 1;
}
else if (comp(val, *middle))
{
len = half;
} else
return middle;
}
return last;
}

template
Iterator BinSearch(Iterator first, Iterator last, T val, Compare comp)
{
return __BinSearch(first, last, val, comp, Compare::CompareTrait());
}

template class TheSimpleCompare : public SimpleCompare
{
public:
bool operator()(const T& lv, const T& rv) const
{ return lv < rv; }
};
template class TheComplexCompare : public ComplexCompare
{
public:
int operator()(const T& lv, const T& rv) const
{ return lv - rv; }
};

typedef TheSimpleCompare SimpleIntCompare;
typedef TheComplexCompare ComplexIntCompare;
/*
class SimpleIntCompare : public SimpleCompare
{
public:
bool operator()(int lv, int rv) const
{ return lv < rv; }
};
class ComplexIntCompare : public ComplexCompare
{
public:
int operator()(int lv, int rv) const
{ return lv - rv; }
};
*/

#define dimof(x) (sizeof(x)/sizeof(x[0]))

int main(int argc, char* argv[])
{
int val = 8;
int tab[] = { 1, 2, 3, 4, 5, 6, 7, 9, 10, 10000};

int *slow = LowerBound(tab, tab + dimof(tab) - 1, val, SimpleIntCompare());
int *clow = LowerBound(tab, tab + dimof(tab) - 1, val, ComplexIntCompare());

int *s = BinSearch(tab, tab + dimof(tab) - 1, val, SimpleIntCompare());
int *c = BinSearch(tab, tab + dimof(tab) - 1, val, ComplexIntCompare());

cout << "*slow = " << *slow << ", *clow = " << *clow << endl;
cout << "*s = " << *s << ", *c = " << *c << endl
<< endl;

return 0;
}

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转载于:http://blog.itpub.net/10794571/viewspace-969600/