Add solution for Challenge 21 by AlexO-85#702

AlexO-85 wants to merge 1 commit intoRezaSi:mainRezaSi/go-interview-practice:mainfrom

AlexO-85:challenge-21-AlexO-85-1762431970AlexO-85/go-interview-practice:challenge-21-AlexO-85-1762431970Copy head branch name to clipboard