参考文献：
http://www.cplusplus.com/reference/algorithm/lower_bound/
http://www.cplusplus.com/reference/algorithm/upper_bound/
两个comp函数的参数位置是不同的，不能直接使用一个comp函数。
lower_bound
Binary function that accepts two arguments (the first of the type pointed by ForwardIterator, and the second, always val), and returns a value convertible to bool. The value returned indicates whether the first argument is considered to go before the second.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.
upper_bound
Binary function that accepts two arguments (the first is always val, and the second of the type pointed by ForwardIterator), and returns a value convertible to bool. The value returned indicates whether the first argument is considered to go before the second.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.