challenging-exercises.md

Medium difficulty

Climbing the Leaderboard - Medium, Success rate: 55.12%
Append and delete - Medium, Success rate: 66.61%

Challenges with a success rate below 90%

Kangaroo - Easy, Success rate: 88.37%
Between Two Sets - Easy, Success rate: 88.75%
Day of the Programmer - Easy, Success rate: 88.33%
Drawing Book - Easy, Success rate: 89.27%
Picking Number - Easy, Success rate: 88.81%
Save the Prisoner - Easy, Success rate: 78.06%
Circular Array Rotation - Easy, Success rate: 78.25%
Sherlock and Squares - Easy, Success: 84.36%