Shogo Murai

Shogo Murai (handle 'semiexp') is a Japanese competitive programmer and engineer/researcher at Preferred Networks, Inc. in Tokyo. He represented Japan at the International Olympiad in Informatics three times, winning a gold medal each year (2010, 2011 and 2012), and later reached the Google Code Jam 2021 World Finals and won silver at GCJ 2022 - a sustained top-tier presence across a decade. He competed for the University of Tokyo in the ICPC and returned to the IOI as the author of the 2018 'Highway Tolls' task. At Preferred Networks he works on machine learning research, co-authoring work on scaling laws and the PLaMo large language model report, and builds open-source puzzle-solving tools such as cspuz.

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• Won gold for Japan at all three IOI appearances (2010 rank 9/708 pts, 2011 rank 14/524, 2012 rank 4/506) - a three-time IOI gold medalist, one of a very small global group.Jul 2012
• Listed on the Preferred Networks PLaMo 2 Technical Report author list (arXiv:2509.04897), tying him to PFN's flagship Japanese LLM program.Sep 2025
• Reached the Google Code Jam 2021 World Finals and took silver at GCJ 2022 (rank 2), showing top-tier global form a decade after his IOI run - competitive programming is a lifelong pursuit, not a school phase.Aug 2022
• Authored the IOI 2018 task 'Highway Tolls'; returned to the olympiad as a problem setter after competing, the classic route from champion to task author.Sep 2018
• Researcher at Preferred Networks, Inc. (Tokyo); sits on the ICPC Asia Pacific Championship 2025 International Judge Committee as JPN judge.Mar 2025
• Runs semiexp.net and 'Algorithmer's note' (a Hatena blog with 251 posts); his handle 'semiexp' spans GitHub, Twitter/X, AtCoder, Codeforces, TopCoder, Qiita and Zenn, making it the reliable key to de-namesake him.Dec 2024
• Co-authored 'A Scaling Law for Synthetic-to-Real Transfer' (arXiv:2108.11018) with PFN colleagues Hiroaki Mikami, Kenji Fukumizu, Taiji Suzuki and others, confirming a research (not only engineering) role on PFN's ML team.Aug 2021
• Built cspuz, an open-source constraint-satisfaction library for pencil puzzles, reused by other competitive programmers - a hobby project that doubles as a niche tool.Dec 2020
• Blog post 'Google Code Jam 2021 World Finals' and puzzle-generator write-ups show he still publishes detailed contest and solver engineering write-ups, not just results.Aug 2021
• Competed for the University of Tokyo; a Codeforces team preview flags his 3 IOI golds and TopCoder target alongside teammate Makoto Soejima.Jul 2013
• Also active under a second AtCoder handle 'theMurai' (algorithm rating 1044), likely a secondary/practice account.Jan 2022