Output and explanation

#1

vector< int > data = { 1, 1, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 6 };
auto lower = std::lower_bound(data.begin(), data.end(), 4);
auto upper = std::upper_bound(data.begin(), data.end(), 4);
for(auto it = lower; it != upper; it++)
cout << *it << ’ ';

#2

it is obvious that output should be
4 4 4

you can read about lower bound and upperbound here
https://en.cppreference.com/w/cpp/algorithm/lower_bound
http://www.cplusplus.com/reference/algorithm/upper_bound/

#3

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