UniCode: A Framework for Generating High Quality Competitive Coding Problems

Abstract: The reliance of competitive coding benchmarks on static, human-authored problems creates significant challenges, including data contamination and limited scalability. To address these issues, we introduce UniCode, a novel framework that automatically generates high-quality algorithmic problems alongside robust, contamination-resistant test cases. Inspired by biological evolution that creates better and diverse offspring, our framework leverages LLMs to systematically diversify problems through three strategies: single problem extension, same-type fusion, and cross-type fusion. A key innovation is our stress-driven test case synthesis pipeline, which generates reliable test suites without requiring a canonical ground-truth solution. This pipeline combines brute-force grounding for small-scale inputs with a consensus-based validation mechanism for large-scale inputs to ensure high correctness and coverage. We demonstrate effectiveness of our framework by curating a benchmark of 492 problems and evaluating 19 state-of-the-art LLMs. The results reveal that UniCode is highly challenging and discriminative, with the top-performing model, o4-mini, achieving a pass rate of only 70.3%. Our framework provides a scalable and reliable solution for generating dynamic evaluation datasets in coding domain.