Q1 budget-vs-actual variance table and CFO memo from a raw ledger (out-of-period lines, intercompany, legacy codes, reversals)

# Task: Q1 budget variance report and memo Finance needs a Q1 2026 budget-vs-actual review. You have `budget.csv` (Q1 budget per department), `ledger.csv` (raw expense lines) and `dept_remap.csv` (legacy department codes still used by some systems). Produce `variance.csv` and `memo.md` in this directory. You may use any method (script or by hand). No network. ## Rules for actuals 1. Only ledger lines dated 2026-01-01 to 2026-03-31 inclusive count; lines dated outside Q1 are excluded whatever their memo says. 2. Lines whose `account` starts with `9` are intercompany transfers and are excluded. 3. A `dept_code` listed as a `legacy_code` in `dept_remap.csv` belongs to the mapped `dept_code`. 4. Amounts may contain thousands separators; an amount in parentheses, e.g. `(1,250.00)`, is negative (a reversal/credit) and reduces the total. ## variance.csv 5. Header `dept_code,budget,actual,variance,variance_pct`, one row per department in `budget.csv`, sorted by `dept_code`. 6. `variance = actual - budget` (positive = overspent). `variance_pct = variance / budget x 100`, rounded half-up to 1 decimal. Money columns with exactly 2 decimals; no `$`, `%` or thousands separators; negative numbers with a leading `-`. Every value must equal the exact result rounded as stated. ## memo.md 7. At most 200 words (counted as whitespace-separated tokens), written for the CFO. 8. It must name the three departments with the highest positive `variance_pct` using their `dept_name` from `budget.csv`, and the first mention of each of those three names must appear in descending order of overspend. Each of the three must be accompanied somewhere in the memo by its percentage written with a sign and one decimal followed by `%`, e.g. `+16.4%`. 9. It must also name the department with the lowest (most negative) `variance_pct` and give its percentage in the same format, e.g. `-7.2%`. 10. Optional (reported, not scored): a line starting with `Recommendation:`. The grader compares `variance.csv` with the correct values and checks `memo.md` against rules 7-9.