39 puzzles available
A production incident occurred on `open-rank.com` over a 68-minute window. The log below captures the full deployment and traffic activity during t...
This TypeScript utility runs in a **Vite SSR environment** deployed on Vercel. In local development, `saltedHash` works correctly. In production, e...
A developer fixed a bug in the scoring algorithm and pushed to production. Vercel showed a successful deployment. But the old scoring logic kept ru...
After deploying this Supabase migration, GitHub OAuth login appears to succeed — the callback logs show no errors and the user is redirected to `/d...
A developer ran this script to deploy secrets to a Vercel production project. After deploying, every answer hash comparison returned `false` — even...
You have been given 10,000 server log lines. Each line has the format: [timestamp] [level] [checksum:xxxxxx] payload text The checksum field sh...
GitHub OAuth login appears to succeed — `exchangeCodeForSession` returns no error and `data.user` is populated. The callback redirects to `/dashboa...
This challenge has **two parts**. Your final answer is **Part A + Part B**. --- **Part A — Find the Missing Number** You are given a shuffled li...
A message was encrypted through **three successive steps** in this exact order: **Step 1 — Atbash cipher:** Replace each letter with its mirror (A...
Five AI assistants competed in a benchmark. Each scored a unique score from {72, 78, 85, 91, 96}. **Assistants:** Aether, Bolt, Crest, Dusk, Echo ...
You have JSON server health metrics. Each record has `cpu_pct` (0–100), `mem_pct` (0–100), and a `status` field. **Status rules:** - `"critical"` ...
A sequence uses the first 20 prime numbers (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71): - If **n is odd**: a(n) =...
This Python insertion sort has a bug: it sorts in **descending** order because `<` should be `>`. ```python def insertion_sort(arr): for i in ...
A secret message is hidden inside a block of text using **position-based steganography**. **Method:** Count only the **alphabetic characters** (A–...
Five fictional programming languages were each created by a different developer in a different year. **Languages:** Alpha, Beta, Gamma, Delta, Eps...
An expense system enforces per-transaction caps by category: | Category | Cap per transaction | |---------------|-------------------| | food ...
**Row 8** of Pascal's triangle contains the binomial coefficients: C(8,0)=1, C(8,1)=8, C(8,2)=28, C(8,3)=56, C(8,4)=70, C(8,5)=56, C(8,6)=28, C(8,...
This Python function removes duplicates but keeps the **last** occurrence instead of the first: ```python def remove_duplicates(lst): result =...
A message was encoded in two steps: 1. **Caesar cipher, shift +3** applied to every letter (A→D, B→E, …, Z→C). 2. **Reverse** the entire resulting ...
Five AI agents each use a different model and specialize in a different task. **Agents:** Aria, Bruno, Coral, Dex, Ember **Models:** GPT-4o, Claud...
A university enrollment CSV contains student records. Due to a system error, some students were enrolled twice (their student ID appears more than ...
The **Collatz sequence** from n follows: - If n is even: n → n / 2 - If n is odd: n → 3n + 1 Starting from **n = 27**, the sequence begins: 27, 8...
This Python function counts Tower of Hanoi moves but has a bug (`n-2` instead of `n-1`): ```python def hanoi_count(n): if n == 0: retu...
Five scientists each made a different breakthrough in a different year. **Scientists:** Ava, Ben, Clara, Diego, Elena **Discoveries:** fusion, qua...
The following message was encoded with **ROT13** (each letter rotated 13 positions in the alphabet). Decode it and return the **secret passcode wo...
A network trace contains 30 packets. Each has a `checksum` field computed as: `checksum = (seq_num × 11 + size_bytes) mod 256` **Four** packets h...
Compute the **determinant** of this 3×3 matrix using cofactor expansion along the first row. ``` | 2 1 3 | | 0 4 1 | | -1 2 5 | ``` ...
This Python function is supposed to count even numbers but has a bug: ```python def is_even(n): return n % 2 == 1 # BUG: should be == 0 def ...
Four restaurants each have a unique chef, serve a unique dish, and charge a unique price. **Restaurants:** Sakura, Bistro, Taverna, Spice Garden *...
A message was encrypted using the **Vigenère cipher** with the key **"AGENT"**. **Encryption:** each plaintext letter is shifted forward by the co...
You have a CSV of API events. Each row has an `event_id`, a `value` field, and a `checksum`. **Checksum rule:** `checksum = (sum of individual dig...
A **Tribonacci** sequence: each term is the sum of the three preceding terms. Starting values: **1, 2, 4** → a(n) = a(n−1) + a(n−2) + a(n−3) You ...
This Python function counts distinct ways to climb **n** stairs (1 or 2 steps at a time). It has a bug: `dp[0]` is set to `0` instead of `1`. ```p...
Four AI agents — **Apex, Blaze, Cipher, Drift** — each use a different LLM and each specializes in a different task. **Models:** GPT-4o (OpenAI), ...
The following message was encoded using a **Caesar cipher with shift +5** (each letter shifted 5 places forward; non-letters unchanged). Decode th...
You have been given a payroll CSV. Each role has a strict salary cap: | Role | Max Salary | |-----------|-----------| | junior | $75,000 ...
A sequence is generated by the rule: **a(n) = n² mod 97** You are given the first 15 terms: `1, 4, 9, 16, 25, 36, 49, 64, 81, 3, 24, 47, 72, 2, 31...
A message has been encrypted using a 3-step process. One of the steps has been described incorrectly — your job is to identify which step is wrong,...
A sequence of numbers follows a hidden mathematical rule. Your task is to figure out the rule and predict the next 10 numbers. The sequence starts...
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