stl_algorithm算法之二分法查找

7.60、template <class ForwardIterator, class T>
ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last, const T& val)
{    
　　ForwardIterator it;
　　iterator_traits < ForwardIterator>::difference_type count, step;
　　count = distance(first,last);
　　while (count > 0)
　　{
　　　　it = first; 
　　　　step = count/2; 
　　　　advance (it,step);
　　　　if (*it<val) { // or: if (comp(*it,val)), for version (2)
　　　　　　first=++it;
　　　　　　count -= step+1;
　　　　}
　　　　else count = step;
　　}
　　return first;
}

7.61、template <class ForwardIterator, class T>
ForwardIterator upper_bound (ForwardIterator first, ForwardIterator last, const T& val)
{
　　ForwardIterator it;
　　iterator_traits<ForwardIterator>::difference_type count, step;
　　count = std::distance(first,last);
　　while (count>0)
　　{
　　　　it = first; step=count/2; std::advance (it,step);
　　　　if (!(val<*it)) // or: if (!comp(val,*it)), for version (2)
　　　　{ 
　　　　　　first = ++it; 
　　　　　　count -= step+1; 
　　　　}
　　　　else count=step;
　　}
　　return first;
}

7.62、template <class ForwardIterator, class T>
pair<ForwardIterator,ForwardIterator>
equal_range (ForwardIterator first, ForwardIterator last, const T& val)
{
　　ForwardIterator it = std::lower_bound (first,last,val);
　　return std::make_pair ( it, std::upper_bound(it,last,val) );
}

7.63、template <class ForwardIterator, class T>
bool binary_search (ForwardIterator first, ForwardIterator last, const T& val)
{    
　　first = std::lower_bound(first,last,val);
　　return (first!=last && !(val<*first));
}