STL provides binary search functions std::lower_bound and std::upper_bound,
but I tend not to use them because I&#39;ve been unable to remember what they do,
because their contracts seem completely mystifying to me.

Just from looking at the names,
I&#39;d guess that &quot;lower_bound&quot; might be short for &quot;last lower bound&quot;,&lt;br&gt;
i.e. the last element in the sorted list that is &lt;= the given val (if any).&lt;br&gt;
And similarly I&#39;d guess &quot;upper_bound&quot; might be short for &quot;first upper bound&quot;,&lt;br&gt;
i.e. the first element in the sorted list that is &gt;= the given val (if any).

But the documentation says they do something rather different from that--
something that seems to be a mixture of backwards and random, to me.
To paraphrase the doc:&lt;br&gt;
    - lower_bound finds the first element that&#39;s &gt;= val&lt;br&gt;
    - upper_bound finds the first element that&#39;s &gt; val

So lower_bound doesn&#39;t find a lower bound at all; it finds the first *upper* bound!?
And upper_bound finds the first *strict upper* bound.

Does this make any sense??
How do you remember it?

All Lower Bound Solutions on Gang of Coders

Total of 1 Lower Bound Solutions

rationale for std::lower_bound and std::upper_bound?