problems

problems/medium/group-transactions/solution.py

@@ -0,0 +1,33 @@
+"""
+Transaction Grouper
+
+You're building a financial dashboard for a budgeting app. Users want
+to see their spending grouped by category with totals, so they can
+understand where their money is going each month.
+
+Example 1:
+    Input: transactions = [
+        {"amount": 50, "category": "food", "date": "2024-01-01"},
+        {"amount": 30, "category": "food", "date": "2024-01-02"},
+        {"amount": 100, "category": "transport", "date": "2024-01-01"}
+    ]
+    Output: {"food": 80, "transport": 100}
+    Explanation: food: 50+30=80, transport: 100
+
+Example 2:
+    Input: transactions = []
+    Output: {}
+    Explanation: No transactions means empty result
+
+Constraints:
+    - Each transaction has "amount" (positive int), "category" (str), "date" (str)
+    - Categories are case-sensitive
+    - Return categories in any order
+    - Amount is always positive
+"""
+
+
+def group_transactions(transactions: list[dict]) -> dict[str, int]:
+    """Return dictionary mapping each category to its total amount."""
+    pass  # Your implementation here
+

problems/medium/group-transactions/tests.py

@@ -0,0 +1,58 @@
+"""Tests for group-transactions."""
+import pytest
+from solution import group_transactions
+
+
+class TestBasicCases:
+    """Test basic functionality with typical inputs."""
+
+    def test_multiple_categories(self):
+        """Test grouping across different categories."""
+        txns = [
+            {"amount": 50, "category": "food", "date": "2024-01-01"},
+            {"amount": 30, "category": "food", "date": "2024-01-02"},
+            {"amount": 100, "category": "transport", "date": "2024-01-01"}
+        ]
+        assert group_transactions(txns) == {"food": 80, "transport": 100}
+
+    def test_single_category(self):
+        """Test all transactions in one category."""
+        txns = [
+            {"amount": 10, "category": "food", "date": "2024-01-01"},
+            {"amount": 20, "category": "food", "date": "2024-01-02"},
+            {"amount": 30, "category": "food", "date": "2024-01-03"}
+        ]
+        assert group_transactions(txns) == {"food": 60}
+
+    def test_single_transaction(self):
+        """Test with just one transaction."""
+        txns = [{"amount": 25, "category": "entertainment", "date": "2024-01-01"}]
+        assert group_transactions(txns) == {"entertainment": 25}
+
+
+class TestEdgeCases:
+    """Test edge cases and boundary conditions."""
+
+    def test_empty_list(self):
+        """Test with no transactions."""
+        assert group_transactions([]) == {}
+
+    def test_case_sensitive_categories(self):
+        """Test that categories are case-sensitive."""
+        txns = [
+            {"amount": 10, "category": "Food", "date": "2024-01-01"},
+            {"amount": 20, "category": "food", "date": "2024-01-02"}
+        ]
+        result = group_transactions(txns)
+        assert result == {"Food": 10, "food": 20}
+
+    def test_many_categories(self):
+        """Test with many different categories."""
+        txns = [
+            {"amount": 1, "category": "a", "date": "2024-01-01"},
+            {"amount": 2, "category": "b", "date": "2024-01-01"},
+            {"amount": 3, "category": "c", "date": "2024-01-01"},
+            {"amount": 4, "category": "d", "date": "2024-01-01"}
+        ]
+        assert group_transactions(txns) == {"a": 1, "b": 2, "c": 3, "d": 4}
+