Highest_Cost_Scenario_Identification

Highest Cost Scenario Identification

This skill covers two question types in the dabstep dataset, both requiring fee calculation from fees.json.

Fee Formula

fee = fixed_amount + rate * transaction_value / 10000

Key data facts (verified from actual files):

• fees.json has 1000 rules; card_scheme is never null
• is_credit: True = credit only, False = debit only, null/None = both credit and debit
• aci field: either [] (empty list, 112 rules) or a non-empty list of letters — never null
• merchant_category_code field: either [] (empty list, 127 rules) or a non-empty list of integers — never null
• ACI values in fee rules: A, B, C, D, E, F only (G does not appear in any fee rule)
• Card schemes: GlobalCard, NexPay, SwiftCharge, TransactPlus

Empty list semantics for this question type: An empty list [] for aci or merchant_category_code means the rule applies to ALL values of that field (same as null for scalar fields). However, for "most expensive ACI/MCC" questions, rules with aci=[] apply equally to every ACI and cannot differentiate which ACI costs more — skip them. Same logic for merchant_category_code=[] in MCC questions.

Question Type 1: Most Expensive MCC

Pattern: "What is the most expensive MCC for a transaction of X euros, in general?"

Algorithm:

1. Load fees.json
2. For every rule, skip if merchant_category_code is empty ([])
3. Compute fee = fixed_amount + rate * X / 10000
4. For each MCC in the rule's list, track the maximum fee seen across all rules
5. Return all MCCs (sorted ascending) that tie for the global maximum fee

Critical: No card_scheme or is_credit filter for "in general" MCC questions. Include ALL fee rules (regardless of card_scheme, is_credit, etc.) — only skip rules with empty merchant_category_code. Do NOT restrict to MCCs listed in merchant_category_codes.csv.

Output format: Comma-separated MCC integers, sorted ascending. Example: 3000, 3001, 7512

import json

with open('fees.json') as f:
    fees = json.load(f)

transaction_value = X  # from question
mcc_max_fees = {}

for rule in fees:
    mcc_list = rule['merchant_category_code']
    if not mcc_list:  # skip [] (applies to all, doesn't differentiate)
        continue
    fee = rule['fixed_amount'] + rule['rate'] * transaction_value / 10000
    for mcc in mcc_list:
        if mcc not in mcc_max_fees or fee > mcc_max_fees[mcc]:
            mcc_max_fees[mcc] = fee

max_fee = max(mcc_max_fees.values())
result = sorted([mcc for mcc, f in mcc_max_fees.items() if f == max_fee])
print(', '.join(str(m) for m in result))

Question Type 2: Most Expensive ACI

Pattern: "For a [credit/debit] transaction of X euros on [CardScheme], what would be the most expensive ACI? In the case of a draw between multiple ACIs, return the ACI with the lowest alphabetical order."

Algorithm:

1. Load fees.json
2. Filter rules: card_scheme == CardScheme
3. Filter by transaction type:
   • Credit transaction: include rules where is_credit is True or None
   • Debit transaction: include rules where is_credit is False or None
4. Skip rules where aci list is empty ([])
5. Compute fee = fixed_amount + rate * X / 10000
6. For each ACI in the rule's list, track the maximum fee seen
7. Return the ACI(s) with the highest fee; if tied, return the alphabetically lowest

CRITICAL — the answer is an ACI letter, NOT a fee amount. The task instructions may show <answer>0.23</answer> as a generic format placeholder — that 0.23 is irrelevant to ACI questions. Your answer must be the ACI letter in a list: ['A'], ['B'], ..., ['F']. Never return a numeric fee value.

Output format: A Python list containing one letter string. Example: ['E']

import json

with open('fees.json') as f:
    fees = json.load(f)

card_scheme = 'NexPay'      # from question
transaction_value = 1       # from question (in euros)
is_credit = True            # True for credit, False for debit

aci_max_fees = {}

for rule in fees:
    if rule['card_scheme'] != card_scheme:
        continue
    # None means applies to all (credit and debit); include for the target type
    if rule['is_credit'] is not None and rule['is_credit'] != is_credit:
        continue
    aci_list = rule['aci']
    if not aci_list:  # skip [] (applies to all, doesn't differentiate)
        continue
    fee = rule['fixed_amount'] + rule['rate'] * transaction_value / 10000
    for aci in aci_list:
        if aci not in aci_max_fees or fee > aci_max_fees[aci]:
            aci_max_fees[aci] = fee

max_fee = max(aci_max_fees.values())
winners = sorted([aci for aci, f in aci_max_fees.items() if f == max_fee])
answer = winners[0]  # alphabetically lowest in case of tie
print([answer])      # output as a list, e.g. ['E']

Common Mistakes

1. Returning the fee amount instead of the ACI letter: The answer is always a letter (e.g., ['E']), never a number like 0.23 or 0.1467. The 0.23 in task format examples is just a generic placeholder unrelated to ACI answers.
2. MCC filtering: Never exclude an MCC just because it's absent from merchant_category_codes.csv. The fee rules are the sole source of truth for MCC questions.
3. Empty lists []: Skip rules where merchant_category_code or aci is [] for these question types — they apply to all values equally and don't differentiate costs by MCC or ACI.
4. is_credit for ACI questions: Include rules with is_credit=None (applies to all transaction types), not only is_credit=True (for credit) or False (for debit).
5. Tie-breaking for ACI: When multiple ACIs share the maximum fee, return the alphabetically first one (e.g., 'A' before 'B').
6. MCC questions — no card_scheme filter: For "in general" MCC questions, do NOT filter by card_scheme or is_credit. All fee rules contribute regardless of scheme.