The lowercase part you have actually won't work for all cases...

What I would do is just have a boolean variable for each condition, and each check will set the appropriate variable to true or...

Generally when you are doing recursion on any kind of collection of items (lists, arrays, even strings) you want to solve the problem for the first element of the collection, then recurse on the...

You shouldn't ever be returning the operators though, only the result of operations or the number value in the node.

In the first branch, after you apply the operator to the two children, you...