cs1120: Notes 15

Upcoming Schedule

• Wednesday, 30 September (10:01am): Problem Set 4
• Wednesday, 6:30-8pm in Olsson 001: ACs' Review Session
• Thursday, 1:30-3pm in Olsson 236A: Extra Office Hours
• Friday, 2 October: Exam 2 out
• Wednesday, 7 October (10:01am): Exam 2 due

Exam 1

Exam 1 will be distributed shortly after the end of class Friday, and due at 10:01am on Wednesday, October 7.

It will cover all of the material in the course through Class 16 (Wednesday, 30 Sept) including:

• Problem Sets 1-4
• Course Book, Chapters 1-8
• Classes 1-16
• GEB Reading

The exam will emphasize understanding the main concepts we have seen in all three of the problem sets, classes, and course book.

To prepare for Exam 1:

• Review any material you are confused on from PS1-4.
• Try the practice exams from previous courses.
• Try exercises in the course book.

Review Session. The ACs will hold a review session Wednesday, 6:30-8pm in Olsson 001 (this is in place of the normal Help Hours scheduled for Wednesdays).

Office Hours. In addition to my regularly scheduled office hours Monday and Tuesday mornings, I will have additional office hours Thursday 1:30-3pm in Olsson 236A. If none of these times work for you, email me to schedule an appointment.

Analyzing Running Time

(define (flatten-commands ll)
  (if (null? ll) ll
      (if (is-lsystem-command? (car ll)) 
           (cons (car ll) (flatten-commands (cdr ll)))
           (flat-append (car ll) (flatten-commands (cdr ll))))))


(define (is-lsystem-command? lcommand)
  (or (is-forward? lcommand)
      (is-rotate? lcommand)
      (is-offshoot? lcommand)))


(define (flat-append lst ll)
  (if (null? lst) ll
       (cons (car lst) (flat-append (cdr lst) ll))))

What is the asymptotic running time of flatten-commands?

Analyzing Recursive Procedures

To determine the asymptotic running time for a recursive procedure:

1. Determine the running times of all other procedures applied in the body.
2. Introduce variables to represent the size of the inputs (e.g., N).
3. Determine the asymptotic running time for the procedure body except for the recursive call (e.g., in Θ(R(N))). If the running time of the body varies over the calls, think carefully about whether you need to use the worst case or average case running time.
4. Determine the number of recursive calls (e.g., K(N)).
5. The overall running time is in Θ(R(N) K(N)).

(define (insert-sort lst cf)
   (if (null? lst) null
      (insert-one (car lst) (insert-sort (cdr lst) cf) cf)))

(define (insert-one el lst cf)
   (if (null? lst) (list el)
       (if (cf el (car lst)) (cons el lst)
           (cons (car lst) (insert-one el (cdr lst) cf)))))