Solution is incorrect for problem 15.22 Scheduling Tutors about elements-of-programming-interviews HOT 2 CLOSED

Hey Jou-Ting,

Thanks for your inquiry. I checked that algorithm in our book but don't see any 
problem of it. Let me explain how our algorithm works as follows:

I will use 'A', 'B', .., as the notations of tutors. Remember that in our 
problem we have limitation that every tutor must stop tutoring for the day at 
most two hours after starting. For your first example,
A 9- 9:30
A 9:30 - 10
A 10 - 10:30
A 10:30 - 11 (A must stop since he/she has tutored for two hours today.)
B 11 - 11:30
C 11 - 11:30

As a result, for the first example, you need three tutors.

For your second example,
A 9 - 9:30
B 9 - 9:30
A 9:30 - 10
B 9:30 - 10
A 10 - 10:30
B 10 - 10:30
A 10:30 - 11 (A must stop since he/she has tutored for two hours today.)
B 10:30 - 11 (B must stop since he/she has tutored for two hours today.)
C 11 - 11:30
D 11 - 11:30
C 12 - 12:30
C 12:30 - 1

As a result, you need four tutors. The strategy I used here is exactly greedy 
method mentioned in the book (i.e., as soon as there is a request that cannot 
be handled by the previously assigned tutors, we choose a new tutor.)

Feel free to ask questions if you have any problem.