What do AC, WA, RE, CE, TLE, MLE, PE, and OLE mean respectively in the informatics competition?

In the context of informatics competitions, particularly those conducted on automated judging systems like those used in the International Olympiad in Informatics (IOI) or platforms such as Codeforces, the acronyms AC, WA, RE, CE, TLE, MLE, PE, and OLE represent specific verdicts on a submitted program's execution. Each is a definitive classification of a failure or success state, providing critical feedback to the contestant about the nature of their solution's divergence from the problem's requirements. Understanding these verdicts is fundamental to competitive programming, as they guide debugging and optimization efforts far more precisely than a simple pass/fail notification.

The most desirable verdict is AC, or Accepted, which indicates the program executed within all constraints and produced correct output for all judged test cases. Conversely, WA, or Wrong Answer, signifies the program ran to completion but produced an incorrect output for at least one test case; this is often the most common verdict, pointing to logical or algorithmic errors. RE stands for Runtime Error, meaning the program crashed during execution due to issues like division by zero, illegal memory access, or an uncaught exception. CE, or Compilation Error, occurs when the source code cannot be compiled into an executable by the system's compiler, typically due to syntax errors or unsupported language features.

Performance constraints are encapsulated by TLE and MLE. TLE, Time Limit Exceeded, means the program did not finish within the allotted time for a test case, indicating an inefficient algorithm or poor complexity. MLE, Memory Limit Exceeded, indicates the program's memory consumption exceeded the permitted limit, often from allocating excessively large data structures. Two less common but specific verdicts are PE and OLE. PE, or Presentation Error, historically indicated technically correct output with incorrect formatting, such as extra or missing spaces; many modern systems now fold this into WA. OLE, Output Limit Exceeded, means the program produced more data than allowed, often resulting from an infinite loop that continues writing output.

The practical implication of this taxonomy is that it structures the debugging process. A contestant receiving a WA must re-examine their algorithm's correctness, while a TLE demands analysis of time complexity and possible optimization. A RE directs attention to code robustness and boundary conditions. These verdicts are not merely labels but diagnostic tools; their specificity allows competitors to systematically isolate faults, transforming a binary outcome into a learning mechanism about computational efficiency, correctness, and resource management within the strict, unambiguous framework of competitive programming.