rStar-Coder: Scaling Competitive Code Reasoning with a Large-Scale
  Verified Dataset
Authors: name: Yifei Liu, name: Li Lyna Zhang, name: Yi Zhu, name: Bingcheng Dong, name: Xudong Zhou, name: Ning Shang, name: Fan Yang, name: Mao Yang

Advancing code reasoning in large language models (LLMs) is fundamentally
limited by the scarcity of high-difficulty datasets, especially those with
verifiable input-output test cases necessary for rigorous solution validation
at scale. We introduce rStar-Coder, which significantly improves LLM code
reasoning capabilities by constructing a large-scale, verified dataset of 418K
competition-level code problems, 580K long-reasoning solutions along with rich
test cases of varying difficulty. This is achieved through three core
contributions: (1) we curate competitive programming code problems and oracle
solutions to synthesize new, solvable problems; (2) we introduce a reliable
input-output test case synthesis pipeline that decouples the generation into a
three-step input generation method and a mutual verification mechanism for
effective output labeling; (3) we augment problems with high-quality,
test-case-verified long-reasoning solutions. Extensive experiments on Qwen
models (1.5B-14B) across various code reasoning benchmarks demonstrate the
superiority of rStar-Coder dataset, achieving leading performance comparable to
frontier reasoning LLMs with much smaller model sizes. On LiveCodeBench,
rStar-Coder improves Qwen2.5-7B from 17.4% to an impressive 57.3%, and
Qwen2.5-14B from 23.3% to 62.5%, surpassing o3-mini (low) by3.1%. On the more
challenging USA Computing Olympiad, our 7B model achieves an average pass@1
accuracy of 16.15%, outperforming the frontier-level QWQ-32B. Code and the
dataset will be released at https://github.com/microsoft/rStar.