There are a total of $n$ classes labeled with the English alphabet ($A$, $B$, $C$, and so on). Some classes are dependent on other classes for compilation. For example, if class $B$ extends class $A$, then $B$ has a dependency on $A$. Therefore, $A$ must be compiled before $B$.

Given a list of the dependency pairs, find the order in which the classes should be compiled.

Constraints:

• Class name should be an uppercase character.
• $0 \leq$ dependencies.length $\leq 676$
• dependencies[i].length $= 2$
• All dependency pairs should be unique.

In the above examples, the arrows represent the relationship between these classes. For example, the arrow $A \rightarrow C$ shows that $C$ extends $A$, and therefore, $C$ is dependent on $A$.

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps us to check if you’re solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.