Solution: Compilation Order

Statement

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 a character.
• $0 \leq$