problems

problems/easy/two-sum/solution.py

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+"""
+Two Sum
+
+You are a cashier at a busy store. A customer wants to pay exactly
+a target amount using exactly two items from their basket.
+
+Given a list of item prices and a target total, find the indices
+of the two items that add up to the target.
+
+Example 1:
+    Input: prices = [2, 7, 11, 15], target = 9
+    Output: [0, 1]
+    Explanation: prices[0] + prices[1] = 2 + 7 = 9
+
+Example 2:
+    Input: prices = [3, 2, 4], target = 6
+    Output: [1, 2]
+
+Constraints:
+    - 2 <= len(prices) <= 10^4
+    - Each price is a positive integer
+    - Exactly one solution exists
+"""
+
+
+def two_sum(prices: list[int], target: int) -> list[int]:
+    """Return indices of two prices that add up to target."""
+    for i in range(len(prices)):
+        for j in range(i+1, len(prices)):
+            if prices[i] + prices[j] == target:
+                return [i,j]

problems/easy/two-sum/tests.py

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+"""Tests for two-sum."""
+import pytest
+from solution import two_sum
+
+
+class TestBasicCases:
+    """Test basic functionality with typical inputs."""
+
+    def test_example_one(self):
+        """Test first example from problem description."""
+        assert sorted(two_sum([2, 7, 11, 15], 9)) == [0, 1]
+
+    def test_example_two(self):
+        """Test second example from problem description."""
+        assert sorted(two_sum([3, 2, 4], 6)) == [1, 2]
+
+    def test_adjacent_elements(self):
+        """Test when answer elements are adjacent."""
+        assert sorted(two_sum([1, 2, 3, 4], 7)) == [2, 3]
+
+
+class TestEdgeCases:
+    """Test edge cases and boundary conditions."""
+
+    def test_same_value_twice(self):
+        """Test with duplicate values that sum to target."""
+        assert sorted(two_sum([3, 3], 6)) == [0, 1]
+
+    def test_first_and_last(self):
+        """Test when answer is first and last elements."""
+        assert sorted(two_sum([2, 4, 6, 8, 10, 7], 9)) == [0, 5]
+
+    def test_negative_numbers(self):
+        """Test with negative numbers in the list."""
+        assert sorted(two_sum([-1, -2, -3, -4, -5], -8)) == [2, 4]