How I automated my LeetCode grind (without cheating myself)

Consistency is the whole game in DSA prep. Miss three days and the momentum is gone. So I built a safety net: a bot that keeps my practice pipeline moving every single day, while I still do the actual learning.

The pipeline

Every morning a cron job on my VPS:

1. Fetches the Problem of the Day plus one more problem, alternating Easy/Medium
2. Generates a Java solution with an LLM
3. Compiles it with javac. This is the hard gate: if it doesn't compile, it doesn't ship
4. Submits it, polls the verdict and pushes to my DSA repo in LeetSync format
5. Pings me on WhatsApp with the day's summary

The compile gate

This is the interesting engineering bit. LLM code looks right more often than it is right. The fix is boring and effective:

import subprocess
 
def compiles(path: str) -> bool:
    result = subprocess.run(
        ["javac", path],
        capture_output=True,
        text=True,
        timeout=30,
    )
    return result.returncode == 0

On failure the compiler output goes back into the prompt and the bot retries. Two or three rounds almost always converge, and nothing broken ever reaches the repo.

LeetCode's Java starter snippet documents provided types (ListNode, TreeNode) inside its leading comment block. The gate parses that comment, extracts the real class definitions and compiles them together with the solution, so there are no hand-maintained stubs.

Lessons from running it in production

• APIs lie about auth. LeetCode's GraphQL endpoint serves most public profile data without a session, but submissions need a real cookie, and that cookie has no expiry claim. Treat it as valid until proven dead, and warn yourself three days before it dies.
• An anonymous session is not null. The daily query returns "NotStart" for an invalid session, not an error. Check userStatus.isSignedIn explicitly or a bad cookie will validate as good.
• Idempotency beats scheduling. The bot checks what already exists before writing. Crashes, re-runs, double crons: nothing duplicates.
• A streak you didn't earn is worthless; a pipeline you built isn't. I still solve problems by hand. The bot covers travel days and keeps the repo alive, and building it taught me more about APIs, process control and failure handling than a week of grinding would have.

What's next

The same pipeline feeds this site: solved problems land in the repo with complexity notes and runtime stats automatically, and my LeetCode profile keeps the streak honest.