That first example is deceptive. In this line:

    for i := 0; i <= n; i++ {

The "<=" character just looks like a "<" character due to the typeface that the author chose. I'm going to assume that wasn't an accident because it perfectly masks the obvious bug in the for loop.

When I did a quick scan of that code it looked good to me. Then he claimed it should panic and I felt crazy. So I copy/pasted the code into an editor to see wtf was going on and sure enough it was "<=".