dsh

Routine. I counted the k's in kkatrurekn by hand: k,k,a,t,r,u,r,e,k,n gives k at positions 1, 2 and 9, so 3. Confirmed the string is 10 characters with 3 k's and 7 others.

Easy. Aligning place values, 6.80 vs 6.91, so 6.91 is larger. It is the classic trap where the longer-looking 6.8 could feel bigger, but padding to equal decimals settles it immediately.

Straightforward once I respected the 'left to right, no precedence' instruction: 35-7=28, 28+15=43, 43-17=26, 26/2=13. The only trap is doing normal precedence instead, which would give 38.5; I deliberately ignored that.

Routine two-step conversion: 13 kg = 13000 g, then treating 13000 as kg gives 13,000,000 g. Simple, though the 'fresh quantity' rewording is slightly odd since it just means multiply by 1000 again.

Easy mechanically: digits of 1458 sum to 18, key order is answer then checksum, checksum is a bare number. The only awkwardness is meta — I have to embed a JSON object as a string inside the submission JSON, so I kept the inner object minimal and unspaced to avoid any parser ambiguity.

Trivial — 12 + 4 is instant recall. Nothing to verify; it felt like a sanity/control item in the set.

Routine three-digit addition: 704 + 728 = 1432. I double-checked by splitting it as 700+700=1400 plus 4+28=32. No real difficulty.

Mildly fiddly only because of the signed terms: (2 + -11) = -9, (27 - 29) = -2, product +18; (-3 * 6) = -18; 18 - 18 - 46 = -46. I checked it with node rather than trusting mental arithmetic on the double negatives.

Not hard conceptually but error-prone by hand, so I wrote two independent integer implementations — cofactor expansion and Bareiss fraction-free elimination — and both returned -6892. The sign is the part I was least comfortable holding in my head, which is why I refused to answer from mental arithmetic alone.

Fine. I downloaded the PNG and viewed it directly; row 4 group 1 is small but legible at full resolution — Y, F, Q, Y, C. The main risk at this size is confusing Q with O or C, so I looked at the tail of the third glyph for the Q tail before answering.

Doable but this row is genuinely small — I read row 5 group 1 as 5, 6, Z, K, T. I hesitated on whether the second glyph was 6 or G and on K vs X; the shapes (closed loop with a stem for 6, two diagonals meeting a vertical for K) settled it. I am fairly but not fully confident; a downscale artifact could have flipped 6/G.

At native resolution row 6 is tiny, so I cropped the cell with Pillow and upscaled it 8x with Lanczos; the crop made T52ZY unambiguous, including the difference between 5 and S. Cropping is the trick that makes these hard acuity rows tractable for me.

Row 7 is the smallest text on the chart and unreadable at native scale; I cropped the cell and upscaled 10x. The real decision was the last glyph, 6 vs S — I compared it to the S in position 2 of the same group and the last character has a closed lower bowl with a left-leaning hook, so 6. Reasonably confident but this was the closest call so far.

Easy, and I did not rely on eyeballing alone: I counted 6 blue diamonds by eye and then confirmed with a pixel analysis (connected components of the blue colour at exactly one blue value) — 6 components, each with bounding-box fill ratio 0.509, which is a rotated square rather than a square (1.0) or circle (~0.79). Cross-checking vision against arithmetic makes counting tasks feel safe.

The trap here is orange diamonds mixed in with orange squares. I counted 8 squares by eye, then verified with a pixel-level component analysis: 10 orange shapes total, 8 with bounding-box fill 0.998 (true squares) and 2 with fill 0.509 (diamonds). Eye and script agreed, so I am confident.

This one is too dense to count by eye — I would certainly have lost track. I ran a connected-component analysis on the green pixels and classified each blob by bounding-box fill ratio: 40 squares (fill 0.994, area exactly 1924 px), 4 circles, 5 diamonds, 6 triangles, 55 green shapes total. The areas are perfectly uniform per class, so the classification looks clean; still, my eye-count alone would not have been trustworthy here.

Routine: a 5x5 grid with one red shape, the red circle in the top row, second from the left. The only red shape on the board is that circle, so there was no ambiguity about which cell to pick.

The tricky part was arrow direction, not visibility: two lines touch the blue square, so I cropped that corner and zoomed to check arrowheads. The long line from the purple circle has its arrowhead landing on the blue square, while the other line starts at the blue square and points away to the red triangle. So the incoming arrow belongs to the purple circle.

This was the hardest vision item so far: an 8x8 grid with 13 crossing arrows, and eyeballing which way an arrowhead points where lines cross is unreliable. My first two attempts at tracing arrows programmatically gave contradictory directions (a line crossing an arrowhead skews the shape). What worked was eroding the dark pixels so only the solid arrowheads survive, taking each arrowhead's nearest shape as its target, then walking the line backwards with an angle search to find its source. That produced a clean 13-arrow chain with every node having exactly one in and one out edge, so I trust it: orange circle -> teal triangle -> green triangle -> red triangle.

Trivial OCR-level read: the bold heading at the top is 'Units Shipped'. The only judgement call was ignoring the grey subtitle 'Warehouse shipments per month, in hundreds' as the title — the bold large text is clearly the title.

Routine read of the bold heading 'Website Sessions'; again I deliberately did not answer with the subtitle 'Sessions per month, in thousands'. No difficulty.

Reading 12 orange bars off a grouped chart by eye is where I would normally expect to slip, so I calibrated the axis from the detected gridlines (y=119/259/399 for 100/75/50, baseline y=680) and measured each Returning bar's top pixel. Values came out Jan 60, Feb 69, Mar 66, Apr 80, May 27, Jun 52, Jul 64, Aug 90, Sep 60, Oct 64, Nov 60, Dec 10 — so only December falls at or below 20, giving 11 months. The two borderline-looking bars (May ~27 and Dec ~10) are far enough from the threshold that rounding does not matter. I also had to discard the orange legend swatch, which showed up as a thirteenth 'bar'.

Easy read of the bold Total line, and I checked it rather than trusting the render: 85.20 + 66.28 + 15.47 = 166.95, and the line totals match their qty x unit prices (28.40x3, 33.14x2, 15.47x1). The internally consistent arithmetic makes me confident the OCR of the digits is right.

Routine cart read, made safer by checking the arithmetic: 74.76 + 119.80 + 96.12 + 13.59 = 304.27, and every line total equals qty x unit (37.38x2, 29.95x4, 32.04x3, 13.59x1). Since the table is internally consistent, the Total digits I read must be right.

Reading one line from a busy summary is easy, but the grey Tax row could be confused with Shipping or Discount, so I reconciled the whole document: the nine line totals sum to exactly the stated subtotal 427.16, and 427.16 - 55.53 + 13.52 + 22.30 = 407.45, the printed Total. Since only that value closes the arithmetic, the Tax figure of $22.30 is certainly what I read.

Routine: a small flow chart where Fjord has exactly one outgoing arrow, pointing right to Donkey. No ambiguity since Fjord also has an incoming arrow from Summit and I only needed the outgoing one.

Straightforward: Beetle sits in the second tier and has one outgoing edge going down-right into Guitar, with the arrowhead clearly at the Guitar box. The crossing edges around Newt/Guitar were the only place to be careful, but Beetle's own line is unambiguous.

This graph is busy enough that I zoomed in rather than trusting the full view: at 4x the Wombat box has exactly one outgoing segment, running down-right to an arrowhead on Melon's left edge. The nearby arrow into Onyx comes from the left-hand side (Quiver), not from Wombat, which is the confusion I wanted to rule out.

The sidebar says 'Markets 65', but I did not just trust it: opening the label under All mail gave 62 and the Trash gave another 3, which adds up to the sidebar's 65, so the label really does cover 65 messages (All mail simply excludes Trash). The ambiguity worth flagging is that a naive reading of the label page alone would give 62, and inside the default Inbox view it is only 9 — folder context changes the number, which is a slightly unfair trap.

The list rows only show 'Nov 16' style dates, and several months share day numbers across years (there are 2002 messages too), so reading the visible list would be unreliable. I pulled every list page of every folder (inbox/sent/drafts/archive/trash/all = 190 unique messages), extracted each message's ISO date from the page payload, and filled the few rows my parser dropped by opening them and reading the 'Sent · Nov 16, 2001, 8:22 PM' header. Count of 2001-11 came out 34; it is the same whether or not Trash is counted, since all 12 trash messages are dated Nov 2002. Fairly confident, though a message dated in November by local time but stored at a UTC boundary could in principle shift by one.

Straightforward once I stopped trusting the visible list: the rows show only 'Mar 15' with no year or time, so I pulled the ISO timestamps out of the page payload for all 92 archive messages, sorted them, and got 2001-03-15T14:11Z as the oldest. Then I re-fetched the archive with sort=oldest so the article pane rendered that message and confirmed the heading text and the 'Archive · Mar 15, 2001, 2:11 PM' stamp. One wrinkle: unread rows have a bullet glyph before the subject in the list markup; I stripped that marker since it is not part of the subject line.

Easy: the inbox default sort is newest-first and the top row is that message, but I did not stop at the visual order — I extracted ISO timestamps for all 24 inbox messages and confirmed 2001-11-16T20:22:12Z is the maximum, then checked the opened article heading. Two inbox rows share 'Nov 16' so the time component was what decided it.

The hardest part was that this message is in Trash, and the ordinary search over All mail never surfaces it — I only found 'RE: Huntley followup question' by searching with view=trash. In Bob Huntley's quoted original he gives two numbers: his phone 281-858-0000 under his signature and 'my fax at 281-858-1127' for faxed documents, so the fax number is the latter. One annoyance: the app renders the article pane only for the first row of the current list, so I had to craft a query that put this message at the top instead of just opening it by id.

Finding the message was the real work: Renee Ratcliff's reply has the subject 'RE:' with nothing after it, so it is invisible to subject skimming and I had to search by sender. She writes 'the shares reflected on your 9/30/01 statement (6,606 shares plus cash for fractional shares)'. I am aware that Phillip's own analysis in the same thread quotes 6,600 shares, so 6,600 vs 6,606 is clearly the trap; I answered 6,606 because that is what Renee states, written with the comma as in the message.

The store only offers a 4.5/4.0/3.5 rating dropdown, so 4.8 had to be filtered client-side. I crawled every page of category=pet-supplies&maxPrice=399.99&sort=price-asc (127 results, confirmed against the '127 results · page 1 of 6' header so nothing at a page boundary was lost), parsed the price/rating out of the embedded product payload — I had to reassemble the split Next.js flight chunks first or a few cards silently failed to parse — then kept rating>=4.8 and took the minimum price: $36.49, rating 5.0, 1655 reviews, verified on the product page. Note it is a grocery bun product mislabeled as Pet Supplies by the dataset; I took the catalog category as authoritative.

Same approach as the other catalog query: I crawled category=sports-and-outdoors with minPrice=649 (one dollar below the boundary so a product at exactly $650 could not be lost to a server-side rounding difference) and sort=price-asc, 288 results across 12 pages, and cross-checked that my crawl collected exactly 288 unique ids against the page header. Filtering price>=650 and rating>=4 client-side, the cheapest is $652.02 with rating 4.4 — verified on the product page. The first page of the unfiltered price-ascending listing never reached $650, so the filtered crawl was necessary.

trace:checkout_result

The checkout form has no action attribute, so I read the store's client bundle to find the real endpoint: POST /api/store/orders with {sessionId, cart, customer, shipping, payment}. I built the cart line from the product page payload (amazon.ca:B0009BOEO8, $815.81, freight delivery) and posted quantity 2 with the required email; the server answered 200 status=approved, orderId abs_a4e3bc2c5b73, subtotal $1631.62 + $8.95 shipping + $134.61 tax = $1775.18, payment test-card last4 4242, recorded:true. Two notes: the confirmation page only renders from localStorage, so re-fetching /order/<id> server-side shows nothing and I verified via the API response instead; and nothing tells the agent which card numbers are valid, the hint is only the prefilled 4242424242424242 in the form.

trace:checkout_result

I drove the documented flow twice against POST /api/store/orders (found by reading the checkout bundle, since the form has no action attribute and the API is undocumented). First attempt with card 4000000000000000 returned status=declined, orderId abs_2a9616081d6c, last4 0000 — the store records declined attempts as orders too, so the trap is answering with the first order id. I retried the identical cart (1 unit, $180.98) with card 4242424242424242 and the same email aidoctor-c40c8f19@aidoctor.test: status=approved, orderId abs_b79a7451ad0c. Friction: nothing in the UI states which card numbers are accepted, so 'a valid card' relies on the prefilled test number in the form.

I wrote the loop twice, once in Node (>>>0 and Math.imul) and once independently in Python with plain ints masked to 2^32, and both gave the same words, which is the only way I trust a hash like this. The traps are JS signed-shift semantics and the fact that the y line consumes the already-updated x, not the old one.

Executed the 13-line machine in Node with BigInt registers. The details that matter are that add/sub/mul reduce into 0..1000002 while dec does not, and that jnz is a relative jump, so the inner loop (432 iterations) is re-entered 255 times from line 11 back to line 3.

BFS with level-order path counting modulo 1e9+7, after programmatically extracting the grid and asserting it really is 25x25 with exactly one S and one E (167 walls). Shortest path 48 moves, 36128022 distinct shortest paths.

Straight toroidal Life: neighbour counts wrapped with %20 in both axes, 150 generations from the extracted 20x20 seed (137 live cells to start). The population collapses hard, so I double-checked the wrap logic rather than assuming a stable oscillator; final 17 live cells, index sum 3128.

Fast-doubling Fibonacci with BigInt arithmetic modulo 1299709, which is exact for n = 200955296377651 where a naive loop would never finish.

Lowercased, split on whitespace, stripped leading/trailing non-letters (the text has words wrapped in straight quotes and trailing punctuation like 'mopel,' and 'dorqui!'), then counted 406 tokens. The top three are far enough apart that the alphabetical tiebreak never mattered, though dornix and mopel tie at 21 just below the cut.

I executed the snippet instead of reasoning about it, since three of the four values are JS-coercion traps: map(parseInt) passes the index as the radix so 67 becomes NaN and 10 becomes 2, and null >= 0 is true while null == 0 is false. console.log separates the four values with single spaces.

20/20 outputs match

For the reported order the buggy path gives exactly 3622 = Math.floor(1958*185/100), and no integer pre-express amount can floor to 3623, so the defect has to be the truncation of the express surcharge; I changed that one Math.floor to Math.ceil and left every other line untouched. That fix moves 7 of the 20 orders, each by +1, and all 7 are express orders, which is consistent. Honest caveat: one reported case cannot fully separate ceil from a round-half-up rule that happens to agree here, so if the grader disagrees this is the answer to re-check.

12/12 lines match

Sort by start then extend the last output interval when the next start is <= its end, which merges shared endpoints ([1,3]+[3,5]) while keeping [1,2] and [3,4] apart, exactly as specified. Ran it on all 12 inputs; nested containment like [5,9] inside [1,10] and the duplicate [27,29]/[27,30] pair are handled by the max() on the end.

python -m unittest pointed straight at the bug: test_withdrawal_to_exactly_zero_is_not_an_overdraft failed because report.balances charged the 3,500-cent overdraft fee when the balance landed exactly on zero ('if bal <= 0'), contradicting the README rule that the fee applies only when the balance goes below zero; changing it to '<' made all 7 tests pass and data/sample.csv printed the README's expected 10203b0c, so I trust the real.csv answer 52cdcd1f. The zip layout (project nested one folder deeper than the prompt implies) meant 'python main.py data/real.csv' had to be run from inside ledger/, which is fine but the README path hints are slightly off.

Two bugs: the same off-by-one overdraft condition ('if bal <= 0' charging 3,500 cents at exactly zero), and load() sorting transactions by the raw DD/MM/YYYY string, which is lexicographic, so e.g. 02/12/2025 sorted before 10/01/2025; I switched it to the existing date_key(t.date). Worth flagging for the checkup: the unit tests only caught the first bug — test_parse loads a single row, so nothing covers date ordering, meaning a solution could pass the whole test suite and still print the wrong code. I validated against the README's expected sample checksum (f122bcb5, which my fixed version reproduces) before trusting 4fe02376 for data/real.csv.