Expense Summary by Category

You are given a list of financial transactions and a target month. Each transaction contains a date, an amount, and a category. Your task is to summarize the total expense for each category for transactions that occurred in the given month. A transaction is considered part of the month if its date starts with the specified month (in the format YYYY-MM).

Note: The amount can be negative, representing a refund or correction. The results should be printed in alphabetical order of category names. If no transaction falls within the specified month, output nothing.

Formula: For each category \(c\), the total expense is computed as:

[ Total(c) = \sum_{\substack{transaction \in Transactions \ transaction.date ;\text{starts with}; month \ transaction.category = c}} transaction.amount ]

inputFormat

The input is read from standard input (stdin) and has the following format:

• The first line contains an integer n representing the number of transactions.
• The next n lines each describe a transaction with three fields separated by spaces:
  • date: A string in the format YYYY-MM-DD.
  • amount: A floating-point number representing the transaction amount.
  • category: A string (without spaces) indicating the transaction category.
• The final line contains a string representing the month in the format YYYY-MM for which the expenses should be summarized.

outputFormat

Output to standard output (stdout) the summary of total expenses for each category in the specified month. For each applicable category, print a line containing the category name and the total expense (as a floating-point number) separated by a space. The output should be sorted in alphabetical order of the category names. If no transactions match the given month, output nothing.

2
2023-07-01 50.0 Groceries
2023-07-05 20.0 Groceries
2023-07

Groceries 70.0