javaEASYCODING
Warm up with collections frequency index diagnostic drill
Easy Java arena: HashMap, sorting, and stable tie breakers
XP reward
140
Coins
12
Target time
42m
A learner is about to attempt the full collections frequency index arena. Build a smaller but realistic diagnostic that exposes whether they understand HashMap, sorting, and stable tie breakers. You are working inside a Java backend interview lab, and the arena only clears when the result is safe, deterministic, and explainable.
Learning objective
Learn to apply HashMap, sorting, and stable tie breakers in a Java backend interview lab while explaining the invariant, safety constraints, and hidden edge cases.
Mission order
Input contains one query term per line with mixed casing. Include one normal case, one malformed case, and one ordering or safety edge case. Implement the direct solution first, then document the one edge case that can break it. Submit the solution plus enough reasoning to pass hidden edge cases.Visible checks
sample case
Expected: 2
empty input
Expected: 0
Clear requirements
- Demonstrates HashMap, sorting, and stable tie breakers
- Handles the visible sample and hidden edge cases
- Keeps output deterministic and explainable
- Avoids unsafe dynamic execution
Secure validation contract
Judge type
CODING
Complexity target
Readable O(n) or O(n log n) baseline
Workspace
Code editor
javasafe mock judge
Charging editor core
Test Results
Run the visible checks when your first pass is ready.
Clear Protocol
1Read the scenario and restate the expected output shape.
2Run visible checks before chasing hidden edge cases.
3Use Genie for one nudge if stuck, then explain the invariant.
4Submit only when the result is deterministic and safe.
Rewards
XP
140
Coins
12
Mission Route
Hints
Hints are metered and logged for No Hint Hero runs.
Genie Mentor Core
Hint protocol / contextual guardrails active
Progressive hints
Failed-test aware
Solution guarded
Mission: java-easy-collections-frequency-diagnostic0 attempts0 failed tests0 hints used
Progressive hint depth
Genie: Genie online. I use your mission, attempts, failed tests, hints, and path context to coach the next rep without dumping answers first.