C++ 算法 中的 lower_bound函数

default (1)       template <class ForwardIterator, class T>
                           ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last,
                               const T& val);
 
custom (2)      template <class ForwardIterator, class T, class Compare>
                         ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last,
                               const T& val, Compare comp);

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{

  vector<int> v = {3, 1, 4, 6, 5};


  decltype(v)::iterator it = lower_bound(v.begin(), v.end(), 4);

  cout << *it << ", pos = " << (it - v.begin()) << endl;
  return 0;
  
}

#include <iostream>    //std::cout
#include <algorithm>   //std::lower_bound, std::upper_bound, std::sort
#include <vector>      //std::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

  sort (v.begin(), v.end());               //10 10 10 20 20 20 30 30

  vector<int>::iterator low,up;
  low=lower_bound (v.begin(), v.end(), 20);//         ^
  up= upper_bound (v.begin(), v.end(), 20);//                  ^

  cout << "lower_bound at position " << (low- v.begin()) << '\n';
  cout << "upper_bound at position " << (up - v.begin()) << '\n';

  return 0;
}

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector> 

using namespace std;
 
template<class ForwardIt, class T, class Compare=less<>>
ForwardIt binary_find(ForwardIt first, ForwardIt last, const T& value, Compare comp={})
{
   //Note: BOTH type T and the type after ForwardIt is dereferenced 
   //must be implicitly convertible to BOTH Type1 and Type2, used in Compare. 
   //This is stricter than lower_bound requirement (see above)
 
    first = lower_bound(first, last, value, comp);
    return first != last && !comp(value, *first) ? first: last;
}

int main() 
{
    vector<int> data = { 1, 1, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 6 };
 
    auto lower = lower_bound(data.begin(), data.end(), 4);
    auto upper = upper_bound(data.begin(), data.end(), 4);
 
    copy(lower, upper, ostream_iterator<int>(cout, " "));
 
    cout << '\n';
 
   //classic binary search, returning a value only if it is present
 
    data = { 1, 2, 4, 6, 9, 10 }; 
 
    auto it = binary_find(data.cbegin(), data.cend(), 4); //< choosing '5' will return end()
 
    if(it != data.cend())
      cout << *it << " found at index "<< distance(data.cbegin(), it);
 
    return 0;
}

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

bool ignore_case(char a, char b) {
   return(tolower(a) == tolower(b));
}

int main(void) {
   vector<char> v = {'A', 'b', 'C', 'd', 'E'};
   auto it = lower_bound(v.begin(), v.end(), 'C');

   cout << "First element which is greater than \'C\' is " << *it << endl;

   it = lower_bound(v.begin(), v.end(), 'C', ignore_case);

   cout << "First element which is greater than \'C\' is " << *it << endl;

   it = lower_bound(v.begin(), v.end(), 'z', ignore_case);

   cout << "All elements are less than \'z\'." << endl;

   return 0;
}