Revenue Report from CSV

Finance sends you an orders export:

order_id,region,amount_cents,status
1001,EU,2599,paid
1002,US,1000,refunded

Return total paid revenue in cents per region as an object/map {region: cents}.

The first line is the header; columns are always in this order.
Trim whitespace around fields; status is case-insensitive (PAID counts).
Skip malformed rows: wrong number of columns, or an amount_cents that isn't a whole number.
Ignore empty lines. Regions with no paid orders are omitted.

Example 1

Input: csv = "order_id,region,amount_cents,status\n1,EU,2599,paid\n2,US,1000,refunded\n3,EU,401,PAID"
Output: {"EU":3000}

Solution and explanation

Show the solution

Time O(size of input) · Space O(regions)

Line-oriented parsing with validation at each step, accumulating integers per region. Negative amounts are valid whole numbers (e.g. adjustments), which is why -200 is summed; 10.5 is rejected because cents must be integers.

Real CSV has quoted fields with embedded commas and newlines — in production use the platform CSV parser (csv in Python, fgetcsv/SplFileObject in PHP, a library in Node/Java) and stream large files row by row.

Reference solution

function revenueByRegion(csv) {
  const totals = {};
  for (const line of csv.split("\n").slice(1)) {
    if (!line.trim()) continue;
    const fields = line.split(",").map((f) => f.trim());
    if (fields.length !== 4) continue;
    const [, region, amount, status] = fields;
    if (!/^-?\d+$/.test(amount) || status.toLowerCase() !== "paid") continue;
    totals[region] = (totals[region] ?? 0) + Number(amount);
  }
  return totals;
}

function revenueByRegion(csv: string): Record<string, number> {
  const totals: Record<string, number> = {};
  const rows = csv.split("\n").slice(1).filter((l) => l.trim() !== "");
  for (const row of rows) {
    const fields = row.split(",").map((f) => f.trim());
    if (fields.length !== 4) continue;
    const [, region, amount, status] = fields;
    if (!/^-?\d+$/.test(amount) || status.toLowerCase() !== "paid") continue;
    totals[region] = (totals[region] ?? 0) + Number(amount);
  }
  return totals;
}

import re

def revenue_by_region(csv: str) -> dict[str, int]:
    totals: dict[str, int] = {}
    for line in csv.split("\n")[1:]:
        if not line.strip():
            continue
        fields = [f.strip() for f in line.split(",")]
        if len(fields) != 4:
            continue
        _, region, amount, status = fields
        if not re.fullmatch(r"-?\d+", amount) or status.lower() != "paid":
            continue
        totals[region] = totals.get(region, 0) + int(amount)
    return totals

<?php

function revenueByRegion(string $csv): array
{
    $totals = [];
    foreach (array_slice(explode("\n", $csv), 1) as $line) {
        if (trim($line) === '') {
            continue;
        }
        $fields = array_map('trim', explode(',', $line));
        if (count($fields) !== 4) {
            continue;
        }
        [, $region, $amount, $status] = $fields;
        if (!preg_match('/^-?\d+$/', $amount) || strtolower($status) !== 'paid') {
            continue;
        }
        $totals[$region] = ($totals[$region] ?? 0) + (int) $amount;
    }
    return $totals;
}

class Solution {
    public Map<String, Integer> revenueByRegion(String csv) {
        Map<String, Integer> totals = new HashMap<>();
        String[] lines = csv.split("\n");
        for (int i = 1; i < lines.length; i++) {
            if (lines[i].isBlank()) continue;
            String[] f = lines[i].split(",", -1);
            if (f.length != 4) continue;
            String region = f[1].trim(), amount = f[2].trim(), status = f[3].trim();
            if (!amount.matches("-?\\d+") || !status.equalsIgnoreCase("paid")) continue;
            totals.merge(region, Integer.parseInt(amount), Integer::sum);
        }
        return totals;
    }
}

Common mistakes

Parsing money with floats.
parseInt("10.5") → 10 in JavaScript — validate with a regex instead.
Hand-splitting quoted CSV in production code.

Follow-up questions

Support quoted fields.
Stream a 5 GB file.
Convert currencies using a rates table.

Example 1

Hints

Write and run your solution

Solution and explanation

Reference solution

Common mistakes

Follow-up questions

Example 1

Hints

Write and run your solution

Solution and explanation

Reference solution

Common mistakes

Follow-up questions

More Data Processing problems