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# Lynbrook Computer Science PowerPoint PPT Presentation

Lynbrook Computer Science. Member Meeting: October 27 th , 2008. American Computer Science League. Two Divisions: Intermediate Senior First Competition: December 19 th , 2008 Short Problem (like CAML) + Programming problem Topics: Boolean Logic Graph Theory Recursion

Lynbrook Computer Science

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## Lynbrook Computer Science

Member Meeting: October 27th, 2008

### American Computer Science League

• Two Divisions:

• Intermediate

• Senior

• First Competition: December 19th, 2008

• Short Problem (like CAML) + Programming problem

• Topics:

• Boolean Logic

• Graph Theory

• Recursion

• Converting between Number Systems (dec, oct, hex, bin)

• Data Structures

### Senior Div. Sample Problems (taken from ACSL website)

BASIC Program:

If the following program prints 15, what was the input?

1input N

2if N > 5 then N = N + 8

3if N > 12 then N = N - 6

4if N >= 8 then N = N + 1

5print N

6end

### BASIC I/O Solution

Work Backwards:

• Line 4: N = 14

• Line 3: N = 20

• Line 2: N = 12

### Here are some more…

Computer Number Systems

• What is the base 16 value of FEDCBA16 – ABCDEF16?

Recursive Functions

• Find f(10, 5) given the following:

• If x > y then f(x, y) = f(x-2, y+1) + 3

• If x < y then f(x, y) = f(x+1, y-3) + 2

• Otherwise, f(x, y) = 5

### Computer Number Systems Solution

• Work from right to left, and borrow as needed:

1A – F = B

1B – E – 1 = C

1C – D – 1 = E

D – C – 1 = 0

E – B = 3

F – A = 5

### Recursive Function Solution

Work through the recursion

• f(10, 5) = f(8, 6) + 3

• f(8, 6) = f(6, 7) + 3

• f(6, 7) = f(7, 4) + 2

• f(7, 4) = f(5, 5) + 3

• F(5, 5) = 5

Going backwards and summing up everything,

### Miscellaneous

• More sample problems available at ACSL.org

• TopCoder competitions:

• Single Round Match (SRM): 10/28 @ 6PM

• TopCoder High School SRM: 10/28 @ 6PM

• Register before 3PM!

• Marathon Match : 10/29-11/5