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Where is Johnny Ho? PowerPoint Presentation
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Where is Johnny Ho?

Where is Johnny Ho?

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Where is Johnny Ho?

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  1. Where is Johnny Ho? Answer: Italy

  2. Three levels: bronze, silver, gold • Starts off in bronze division • Do well and be promoted to silver and gold • 16 finalists in gold go to USACO training camp • 4 chosen for US team to go to IOI • 6 contests throughout the year • Nov, Dec, Jan, Feb, Mar, Apr

  3. Held 3-4 times a year • At Gunn, Harker, (possibly Monta Vista), and Stanford • Teams of 3 people solve 12 problems in 2 hours • 4 each of 2 point, 5 point, and 9 point problems • Top 3 teams win prizes! • Free food!

  4. Contests: More Contests • Quixey Challenge • Short program written in python with 1 line bug. • 1 bug, 1 minute, $100. • Online contests held every 1-2 weeks. • Varying difficulty. • Extensive problem set. • Many online contests. • Win cash prizes! • Software companies recruit people here.

  5. Euclidean Algorithm (GCD) • Find greatest common divisor of two numbers • From Euclid’s book Elements • Oldest nontrivial algorithm • O(log n) runtime complexity • This means it’s FAST!!!!! • Key observation: GCD (x, x+y) = GCD (x, y) • Example: find GCD (162, 234) • Use the Euclidean Algorithm! • GCD (162, 234) = GCD (162, 72) • GCD (72, 162) = GCD (72, 90) = GCD (72, 18) • 72 = 4 x 18

  6. Euclidean Algorithm Code • Implementation (very short!) public intgcd (int a, int b) { if (b == 0) { return a; } else { return gcd(b, a % b); } }

  7. Problem of the Week • Problems related to that week’s lecture • Yes, this week’s PotW will be on GCD! • Concepts and tricks for USACO and other contests • Will be posted on our website at lynbrookcs.com • Varying difficulties and points • Graded based on guidelines specified in problem • Officers reserve the right to grade as they please :] • Code should run in one second • About 100-500 million operations • Email solutions to potw@lynbrookcs.com by Sunday 11:59 PM • Any programming language accepted • Console input/output (System.in, System.out) unless otherwise specified • Submit as many times as you want • Solution will be presented at next meeting • See your score at lynbrookcs.com/potw • Feedback is always welcome • Earn Prizes!

  8. First PotW of the Year! • Farmer Johnny Ho has N gold medals and M t-shirts • He wants to divide them into identical groups • All groups must have the same number of t-shirts • All groups must have the same number of medals. • He has too many of both so he is having a hard time trying to figure out how many different ways he can divide them. Help him out! • Example: N = 6, M = 4. • Farmer Johnny Ho can do this in two ways. • 1 group of 6 medals and 4 t-shirts • 2 groups of 3 medals and 2 t-shirts • Constraints: • Easy (10 points): N < 100, M < 100 • Medium (20 points): N < 10000, M < 10000 • Hard (25 points): N ^ 109, M < 109

  9. Hints! • How to read input and print output JAVA: import java.util.*; ... Scanner in; in = new Scanner(System.in); int N = in.nextInt(); int M = in.nextInt(); System.out.println(N+M); C++: #include <iostream> using namespace std; ... int N, M; cin >> N >> M; cout << N+M << endl;