Chapter 21 Exercise 7 Fix

[ghost]

I'm learning C++ and like to use your github to check my work/improve. Overall it is very well done and thank you for sharing!

The issue in your bin_lst() function is that it will not check against the exactly middle or exactly last element in a container.
So if you have a list{1,2,3,4,5,6,7,8,9,10}; , the function will not find 5 or 10. If you add the following code, it should work better. Your bin_lst() function will also work directly with vector as well.

I'm new to Github, so sorry if my formatting is subpar. If you add :

if (half == 0 && *(--last) == val)
        return last;

just after the loop at line 60, it will fix your code. It's the best I can manage, so I'm not sure if there's a better solution.

`template<typename Iter, typename T>
Iter bin_lst(Iter first, Iter last, const T& val)
{
auto half = std::distance(first, last);
auto end = last;

while (first != last && half != 0) {
    if (*first == val) return first;

    half /= 2;
    auto mid = first;
    std::advance(mid, half);
    *mid > val
        ? std::advance(last, -half)
        : std::advance(first, half);
}

//loop exits when half = 0
//but last value wasn't checked
if (half == 0 && *(--last) == val)
return last;

return end;

}`