获取低区间, 在容器必须想sort 排序
template <class ForwardIterator, class T>
ForwardIterator lower_bound ( ForwardIterator first, ForwardIterator last, const T& value )
{
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<value) // or: if (comp(*it,value)), for the comp version
{ first=++it; count-=step+1; }
else count=step;
}
return first;
}
// lower_bound/upper_bound example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main () {
int myints[] = {10,20,30,30,20,10,10,20};
vector<int> v(myints,myints+8); // 10 20 30 30 20 10 10 20
vector<int>::iterator low,up;
sort (v.begin(), v.end()); // 10 10 10 20 20 20 30 30
low=lower_bound (v.begin(), v.end(), 20); // ^
up= upper_bound (v.begin(), v.end(), 20); // ^
cout << "lower_bound at position " << int(low- v.begin()) << endl;
cout << "upper_bound at position " << int(up - v.begin()) << endl;
return 0;
}