Finish problem 0002-add-two-numbers

problems/0002-add-two-numbers/solution.py

@@ -0,0 +1,21 @@
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+
+class Solution:
+    def addTwoNumbers(self, l1: ListNode | None, l2: ListNode | None) -> ListNode | None:
+        dummy = ListNode()
+        curr = dummy
+        carry = 0
+        while l1 or l2 or carry:
+            v1 = l1.val if l1 else 0
+            v2 = l2.val if l2 else 0
+            digit = (v1 + v2 + carry) % 10
+            carry = (v1 + v2 + carry) // 10
+            curr.next = ListNode(digit)
+            curr = curr.next
+            l1 = l1.next if l1 else None
+            l2 = l2.next if l2 else None
+        return dummy.next

problems/0002-add-two-numbers/solution_test.py

@@ -0,0 +1,30 @@
+import pytest
+from solution import ListNode, Solution
+
+
+def build(vals):
+    head = None
+    for v in reversed(vals):
+        head = ListNode(v, head)
+    return head
+
+
+def to_list(node):
+    out = []
+    while node:
+        out.append(node.val)
+        node = node.next
+    return out
+
+
+@pytest.mark.parametrize(
+    "l1,l2,expected",
+    [
+        ([2, 4, 3], [5, 6, 4], [7, 0, 8]),
+        ([0], [0], [0]),
+        ([9, 9, 9, 9, 9, 9, 9], [9, 9, 9, 9], [8, 9, 9, 9, 0, 0, 0, 1]),
+    ],
+)
+def test_add_two_numbers(l1, l2, expected):
+    result = Solution().addTwoNumbers(build(l1), build(l2))
+    assert to_list(result) == expected