Match Editorials

Match summary

Round 1 of 2009 TCHS Tournament attracted 399 competitors, which is more than twice the number of participants in 2008 TCHS Tournament. With at most 500 advancers to Round 2 it was enough to get a positive score to advance, and nearly 90% of the participants managed to accomplish this. The round was much easier than a regular HS match, and some competitors were done with all 3 problems in as little as 20 minutes.

decowboy took the lead after the coding phase due to the fastest total time on the problems, with tourist and Zuza closely following. The challenge phase brought neal_wu +25 points and the win. decowboy and tourist took second and third places, respectively.

The Problems

Value	250
Submission Rate	353 / 386 (91.45%)
Success Rate	329 / 353 (93.20%)
High Score	merc90 for 249.44 points (1 mins 20 secs)
Average Score	201.92 (for 329 correct submissions)

If you stand still, it will take you L/Ve minutes to reach the bottom of the escalator. If you prefer to walk instead, it will take you L/(Ve+Vy) minutes, so you will arrive to the station t₁=(L/Ve - L/(Ve+Vy)) minutes earlier. This will allow you to catch an earlier train if it arrives not earlier than t₁ minutes before the moment of your arrival to the station if you choose to stand on the escalator. As follows from the statement, the probability of this event is equal to t₁/T.

Note that if t₁ is greater than T, you will catch an earlier train for sure, so the probability of this event is 1 instead of t₁/T. Most of the failed submissions on this problem either didn't consider this special case or processed it in a wrong way.

Value	500
Submission Rate	336 / 386 (87.05%)
Success Rate	312 / 336 (92.86%)
High Score	xiaowuc1 for 492.96 points (3 mins 24 secs)
Average Score	384.67 (for 312 correct submissions)

Since the debtors turn out to be unreliable independently, the expected profit for the set of loans is simply the sum of expected profits for each individual loan. If the debtor turns out to be unreliable, he returns no money, and the bank loses the amount loaned out to him. If the debtor is reliable, he returns both the base amount of the loan and the interest, so the bank gets a profit equal to the amount of the interest. Thus, the expected profit for each loan is PROB/100 * (-AMOUNT) + ( 1 - PROB/100 ) * ( INTEREST ).

To find out the value of PROB for the loan, one had to map the value of CLASS for the loan to a corresponding value of PROB using the information given in riskClasses. This could be done either by using a map with CLASS as a key and PROB as a value or in a more straightforward manner - by storing CLASS and PROB in different arrays and iterating through them to find the wanted CLASS.

Value	1000
Submission Rate	237 / 386 (61.40%)
Success Rate	219 / 237 (92.41%)
High Score	v3ctor for 964.24 points (5 mins 30 secs)
Average Score	719.54 (for 219 correct submissions)

First, let's have a look at the representation of the position in the maze and moving between positions. The position in the maze can be described with three parameters: x and y coordinates of the cell (its row and column, respectively) and the direction you're facing. A convenient way to describe the direction is a pair (dx, dy), dx and dy being the changes in x and y coordinates that will take place if you move one cell in this direction (thus, facing south corresponds to (1,0), west - to (0,-1) etc). The three kinds of moves are represented as follows:

• moving forward 'F' updates the coordinates without changing the direction: x_F = x + dx, y_F = y + dy;
• turning left and right 'L' and 'R' updates the direction without changing the coordinates: dx_L = - dy, dy_L = dx or dx_R = dy, dy_R = - dx.