equals와 hashCode로 연습하기

In the Solution class, fix the equals/hashCode methods according to the implementation rules for these methods (use your favorite search engine to check the details). Both the first and last strings should be involved in the equals method's comparison and the calculation of the hashcode. The main me

Solution objects are not being compared correctly. Find the bug and fix it. The main method is not tested.

Correct the implementation errors in the Solution's classes equals and hashCode methods.