Cat Gacha: Clean Contaminated Logs and Estimate Pull Probabilities

The challenge

How rare is your favorite cat? Clean up the community's pull logs and estimate the odds. Try it without the answer metadata first, then compare your estimates with the game settings.

Start here

Open the SharePoint folder linked above. challenge/blind_gachaPullData.zip contains six blind JSON exports; loose copies are under challenge/blind_gachaPullData/gachaPullData. The names run from gacha-pulls-2025-09-06_blind.json through the numbered (1) to (5) variants.

The answers folder contains six matching JSON exports with metadata, analysisScript.py, metdata_stripper.py, exampleAnalysis.zip, and CatGameGachaPullsCorrect.pdf. Read the file beginnings and endings as text before calling a JSON parser. Save the answer metadata for the final comparison.

Try it

1. Extract the actual pulls object and document the surrounding non-data text.

2. Determine whether the six files are independent sessions or cumulative snapshots.

3. Produce one clean pull table and a probability estimate for every card, including rare cards.

4. Compare estimates and 95% intervals with the configured probabilities after revealing the answers.

What to build

Build a cleaned JSON object or CSV with id, timestamp, result, and pullNumber; a duplicate and contamination report; and a card-frequency table with counts, total pulls, estimated odds, and intervals. Include a brief explanation of what the data can say about fairness.