lower_bound 和 upper_bound

Return iterator to lower bound

Returns an iterator pointing to the first element in the range [first,last) which does not compare less than val.

Return iterator to upper bound

Returns an iterator pointing to the first element in the range [first,last) which compares greater than val.

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

int main () {
  int myints[] = {10,20,30,30,20,10,10,20};
  std::vector<int> v(myints,myints+8);           // 10 20 30 30 20 10 10 20

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

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

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

  return 0;
}

Output:

lower_bound at position 3
upper_bound at position 6