stl lower_bound upper_bound binary_search equal_range

自己按照stl实现了一个：

 

http://www.cplusplus.com/reference/algorithm/binary_search/ 这里有个注释，如何判断两个元素相同：

Two elements, a and bare considered equivalent if (!(a<b) && !(b<a))

lower_bound返回!(*it<val) ,所以binary_search 只要再判断 !(val<*it) 即可。

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));
}

#include<cstdio>
#include<iostream>
#include<string>
#include<algorithm>
#include<iterator>
#include<sstream>//istringstream
#include<cstring>

using namespace std;

//return first element >=

int * lowerbound(int *first, int* last, int value)
{
    int* it;
    int count=last-first;
    int step;
    while(count>0)
    {
        it=first;
        step=count/2;
        it+=step;
        //it指向的<, ++后排除<
        if(*it<value)
        {
            first=++it;
            count-=step+1;
        }
        else//左边
            count=step;

    }
    return first;
}

//return first element >
int* upperbound(int *first, int *last, int value)
{
    int count=last-first;
    int step;
    int *it;
    while(count>0)
    {
        step=count/2;
        it=first+step;
        //it指向 <= ,++后排除<=
        if(!(value<*it))
        {
            first=++it;
            count-=step+1;
        }
        else
        {
            count=step;
        }
    }
    return first;
}

int main()
{
    int a[]={ 1, 1, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 6 };
    int *lb=lowerbound(a, a+sizeof(a)/sizeof(int), 4);
    cout<<*lb<<endl;

    int *ub=upperbound(a, a+sizeof(a)/sizeof(int), 4);
    cout<<*ub<<endl;
    return 0;
}