US Open 2015 Contest -- Final Results

This was the fourth and final contest of our 2014-2015 contest season, serving as our national championship.

A total of 1384 participants submitted at least one solution, hailing from 69 different countries:

  655 USA   92 CHN   54 IRN   47 GEO   45 CAN   42 BLR   31 IND
   30 VNM   29 TUR   22 BGD   21 KAZ   15 RUS   15 MEX   14 TKM
   13 UKR   13 TJK   12 TUN   12 FRA   12 BGR   12 ARM   11 KOR
   10 THA    9 GRC    9 AUS    8 POL    8 JPN    7 TWN    6 MYS
    6 HRV    6 CUB    6 COL    5 SYR    5 SGP    5 ROU    5 NLD
    5 MKD    5 ISR    5 FIN    5 DEU    5 CZE    4 LVA    4 EST
    4 EGY    4 BRA    4 AUT    3 ZAF    3 NZL    3 MDA    3 IDN
    3 CYP    3 ARG    2 VEN    2 SVK    2 SRB    2 LTU    2 ITA
    2 IRL    2 HUN    2 GBR    2 BIH    2 BEL    2 AZE    1 SVN
    1 PER    1 PAK    1 LUX    1 KGZ    1 ESP    1 ALB

The average participant submitted solutions for 1.8 problems. In total, there were 2507 graded submissions, broken down by language as follows:

  984 C++
  670 Java
  594 C++11
   96 Pascal
   53 Python 3.4.0
   49 Python 2.7.6
   34 C

Below are the detailed results for each of the gold, silver, and bronze contests. You will also find solutions and test data for each problem, and by clicking on any problem you can practice re-submitting solutions in "analysis mode". If you are logged in, you will also see your own specific results below alongside the contest you took.

USACO 2015 US Open, Gold

The Gold division had 395 total participants, of whom 306 were pre-college students. We saw an impressive showing from many countries, with 38 total perfect scores in the pre-college group (12 from the USA!), listed here; congratulations to all of these individuals for their strong results! Overall, the distribution had a reasonable spread:

Note that due to the interactive nature of the googol problem, no test data is available for that problem.


View problem  | (no test data provided)   |   Solution


Palindromic Paths
View problem  |   Test data   |   Solution


Trapped in the Haybales (Gold)
View problem  |   Test data   |   Solution

USACO 2015 US Open, Silver

The Silver division had 475 total participants, of whom 419 were pre-college students. The silver division proved to be quite challenging, with a handful of perfect scores, but overall a somewhat lower distribution:

All competitors who scored 600 or higher on this contest are automatically promoted to the gold division -- congratulations to you all on your strong results! Detailed results for those promoted are here.


Bessie Goes Moo
View problem  |   Test data   |   Solution


Trapped in the Haybales (Silver)
View problem  |   Test data   |   Solution


Bessie's Birthday Buffet
View problem  |   Test data   |   Solution

USACO 2015 US Open, Bronze

The Bronze division had 514 total participants, of whom 416 were pre-college students. Like silver, the bronze contest appeare to be quite challenging this time around:

All competitors who scored 600 or higher on this contest are automatically promoted to the silver division -- to all who were promoted, congratulations! Detailed results for those promoted are here.


View problem  |   Test data   |   Solution


Bessie Gets Even
View problem  |   Test data   |   Solution


Trapped in the Haybales (Bronze)
View problem  |   Test data   |   Solution


Palindromic Paths (Bronze)
View problem  |   Test data   |   Solution

Final Remarks

This contest closes out what I think has been a very successful season! We've seen remarkable effort and results on the part of thousands of individuals participating througouth the season. For the US Open contest in particular, I'm quite happy with the outcome. For those who remember the carnage resulting from the difficulty of last-year's US Open, we intentionally tried to make the difficulty level a bit more accessible this year, albeit while still preserving a good level of challenge. From the distributions above, I think this goal was accomplished. Technically, everything ran reasonably smoothly; there was a tiny bit of confusion -- but nothing too dramatic -- regarding terse grader messages for the gold 'googol' problem (e.g., "line too short" occuring when a program crashed or didn't have appropriate output buffering, causing its output not to reach the grader). We will try to give more descriptive feedback in future interactive problems of this sort.

As this contest marks the end of our season, the USACO staff will now begin deliberation on who to invite as finalists for our 2015 summer training camp. Performance on all USACO contests throughout the year, as well as progress on our training pages, will be considered.

USACO contests are designed to challenge even the very best students, and it can take a good deal of hard work to excel at them. Remember that the more practice you get, the better your algorithmic coding skills will become! To help you fix any bugs in your code, you are encouraged to consult the official solutions above and to make use of "analysis mode" to re-submit improved versions of your solutions.

A large number of people contribute towards the quality and success of USACO contests. Those who helped with this contest include Mark Gordon, Richard Peng, Travis Hance, and Nick (Huaiyu) Wu. I'd like to single out Mark Gordon in particular to thank him for this outstanding contributions this season -- he single-handedly re-wrote our problem management platform and played a leading role in the formulation of every single contest! Thanks also to Amy Quispe for helping to maintain our social media presence (Facebook:, Twitter: (, our translators for allowing us to offer this contest in five additional languages, to Clemson CCIT for providing our main contest server, and to our sponsors for their generous support: Usenix, Jump Trading, Dropbox, and D.E. Shaw.

We thank everyone who has participated this season, and hope they have had an enjoyable and productive experience. We look forward to seeing you all next fall in our next season. Wish us luck as we choose our national teem and compete this summer at the IOI in Kazhakstan!

Happy coding!

- Brian Dean ([email protected])
Director, USA Computing Olympiad
Associate Professor of Computer Science, Clemson University

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