diff --git a/src/holt59/aoc/2023/day1.py b/src/holt59/aoc/2023/day1.py
index 3acd9ad..9fe88f7 100644
--- a/src/holt59/aoc/2023/day1.py
+++ b/src/holt59/aoc/2023/day1.py
@@ -1,27 +1,9 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
-
-lookups_1 = {str(d): d for d in range(1, 10)}
-lookups_2 = lookups_1 | {
-    d: i + 1
-    for i, d in enumerate(
-        (
-            "one",
-            "two",
-            "three",
-            "four",
-            "five",
-            "six",
-            "seven",
-            "eight",
-            "nine",
-        )
-    )
-}
+from ..base import BaseSolver
 
 
-def find_values(lookups: dict[str, int]) -> list[int]:
+def find_values(lines: list[str], lookups: dict[str, int]) -> list[int]:
     values: list[int] = []
 
     for line in filter(bool, lines):
@@ -41,5 +23,27 @@ def find_values(lookups: dict[str, int]) -> list[int]:
     return values
 
 
-print(f"answer 1 is {sum(find_values(lookups_1))}")
-print(f"answer 2 is {sum(find_values(lookups_2))}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]:
+        lookups_1 = {str(d): d for d in range(1, 10)}
+        lookups_2 = lookups_1 | {
+            d: i + 1
+            for i, d in enumerate(
+                (
+                    "one",
+                    "two",
+                    "three",
+                    "four",
+                    "five",
+                    "six",
+                    "seven",
+                    "eight",
+                    "nine",
+                )
+            )
+        }
+
+        lines = input.splitlines()
+
+        yield sum(find_values(lines, lookups_1))
+        yield sum(find_values(lines, lookups_2))
diff --git a/src/holt59/aoc/2023/day2.py b/src/holt59/aoc/2023/day2.py
index a768318..9d1a05c 100644
--- a/src/holt59/aoc/2023/day2.py
+++ b/src/holt59/aoc/2023/day2.py
@@ -1,43 +1,43 @@
 import math
-import sys
-from typing import Literal, TypeAlias, cast
+from typing import Any, Iterator, Literal, TypeAlias, cast
+
+from ..base import BaseSolver
 
 CubeType: TypeAlias = Literal["red", "blue", "green"]
 
 MAX_CUBES: dict[CubeType, int] = {"red": 12, "green": 13, "blue": 14}
 
-# parse games
-lines = sys.stdin.read().splitlines()
-games: dict[int, list[dict[CubeType, int]]] = {}
-for line in filter(bool, lines):
-    id_part, sets_part = line.split(":")
 
-    games[int(id_part.split(" ")[-1])] = [
-        {
-            cast(CubeType, s[1]): int(s[0])
-            for cube_draw in cube_set_s.strip().split(", ")
-            if (s := cube_draw.split(" "))
-        }
-        for cube_set_s in sets_part.strip().split(";")
-    ]
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]:
+        lines = input.splitlines()
+        games: dict[int, list[dict[CubeType, int]]] = {}
+        for line in filter(bool, lines):
+            id_part, sets_part = line.split(":")
 
-# part 1
-answer_1 = sum(
-    id
-    for id, set_of_cubes in games.items()
-    if all(
-        n_cubes <= MAX_CUBES[cube]
-        for cube_set in set_of_cubes
-        for cube, n_cubes in cube_set.items()
-    )
-)
-print(f"answer 1 is {answer_1}")
+            games[int(id_part.split(" ")[-1])] = [
+                {
+                    cast(CubeType, s[1]): int(s[0])
+                    for cube_draw in cube_set_s.strip().split(", ")
+                    if (s := cube_draw.split(" "))
+                }
+                for cube_set_s in sets_part.strip().split(";")
+            ]
 
-# part 2
-answer_2 = sum(
-    math.prod(
-        max(cube_set.get(cube, 0) for cube_set in set_of_cubes) for cube in MAX_CUBES
-    )
-    for set_of_cubes in games.values()
-)
-print(f"answer 2 is {answer_2}")
+        yield sum(
+            id
+            for id, set_of_cubes in games.items()
+            if all(
+                n_cubes <= MAX_CUBES[cube]
+                for cube_set in set_of_cubes
+                for cube, n_cubes in cube_set.items()
+            )
+        )
+
+        yield sum(
+            math.prod(
+                max(cube_set.get(cube, 0) for cube_set in set_of_cubes)
+                for cube in MAX_CUBES
+            )
+            for set_of_cubes in games.values()
+        )
diff --git a/src/holt59/aoc/2023/day3.py b/src/holt59/aoc/2023/day3.py
index db1fff4..ae72053 100644
--- a/src/holt59/aoc/2023/day3.py
+++ b/src/holt59/aoc/2023/day3.py
@@ -1,53 +1,53 @@
 import string
-import sys
 from collections import defaultdict
+from typing import Any, Iterator
+
+from ..base import BaseSolver
 
 NOT_A_SYMBOL = "." + string.digits
 
-lines = sys.stdin.read().splitlines()
 
-values: list[int] = []
-gears: dict[tuple[int, int], list[int]] = defaultdict(list)
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]:
+        lines = input.splitlines()
 
-for i, line in enumerate(lines):
-    j = 0
-    while j < len(line):
-        # skip everything until a digit is found (start of a number)
-        if line[j] not in string.digits:
-            j += 1
-            continue
+        values: list[int] = []
+        gears: dict[tuple[int, int], list[int]] = defaultdict(list)
 
-        # extract the range of the number and its value
-        k = j + 1
-        while k < len(line) and line[k] in string.digits:
-            k += 1
+        for i, line in enumerate(lines):
+            j = 0
+            while j < len(line):
+                # skip everything until a digit is found (start of a number)
+                if line[j] not in string.digits:
+                    j += 1
+                    continue
 
-        value = int(line[j:k])
+                # extract the range of the number and its value
+                k = j + 1
+                while k < len(line) and line[k] in string.digits:
+                    k += 1
 
-        # lookup around the number if there is a symbol - we go through the number
-        # itself but that should not matter since it only contains digits
-        found = False
-        for i2 in range(max(0, i - 1), min(i + 1, len(lines) - 1) + 1):
-            for j2 in range(max(0, j - 1), min(k, len(line) - 1) + 1):
-                assert i2 >= 0 and i2 < len(lines)
-                assert j2 >= 0 and j2 < len(line)
+                value = int(line[j:k])
 
-                if lines[i2][j2] not in NOT_A_SYMBOL:
-                    found = True
+                # lookup around the number if there is a symbol - we go through the number
+                # itself but that should not matter since it only contains digits
+                found = False
+                for i2 in range(max(0, i - 1), min(i + 1, len(lines) - 1) + 1):
+                    for j2 in range(max(0, j - 1), min(k, len(line) - 1) + 1):
+                        assert i2 >= 0 and i2 < len(lines)
+                        assert j2 >= 0 and j2 < len(line)
 
-                    if lines[i2][j2] == "*":
-                        gears[i2, j2].append(value)
+                        if lines[i2][j2] not in NOT_A_SYMBOL:
+                            found = True
 
-        if found:
-            values.append(value)
+                            if lines[i2][j2] == "*":
+                                gears[i2, j2].append(value)
 
-        # continue starting from the end of the number
-        j = k
+                if found:
+                    values.append(value)
 
-# part 1
-answer_1 = sum(values)
-print(f"answer 1 is {answer_1}")
+                # continue starting from the end of the number
+                j = k
 
-# part 2
-answer_2 = sum(v1 * v2 for v1, v2 in filter(lambda vs: len(vs) == 2, gears.values()))
-print(f"answer 2 is {answer_2}")
+        yield sum(values)
+        yield sum(v1 * v2 for v1, v2 in filter(lambda vs: len(vs) == 2, gears.values()))
diff --git a/src/holt59/aoc/2023/day4.py b/src/holt59/aoc/2023/day4.py
index 3cc9d6c..a29caac 100644
--- a/src/holt59/aoc/2023/day4.py
+++ b/src/holt59/aoc/2023/day4.py
@@ -1,5 +1,7 @@
-import sys
 from dataclasses import dataclass
+from typing import Any, Iterator
+
+from ..base import BaseSolver
 
 
 @dataclass(frozen=True)
@@ -9,33 +11,34 @@ class Card:
     values: list[int]
 
 
-lines = sys.stdin.read().splitlines()
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]:
+        lines = input.splitlines()
 
-cards: list[Card] = []
-for line in lines:
-    id_part, e_part = line.split(":")
-    numbers_s, values_s = e_part.split("|")
-    cards.append(
-        Card(
-            id=int(id_part.split()[1]),
-            numbers=[int(v.strip()) for v in numbers_s.strip().split()],
-            values=[int(v.strip()) for v in values_s.strip().split()],
-        )
-    )
+        cards: list[Card] = []
+        for line in lines:
+            id_part, e_part = line.split(":")
+            numbers_s, values_s = e_part.split("|")
+            cards.append(
+                Card(
+                    id=int(id_part.split()[1]),
+                    numbers=[int(v.strip()) for v in numbers_s.strip().split()],
+                    values=[int(v.strip()) for v in values_s.strip().split()],
+                )
+            )
 
-winnings = [sum(1 for n in card.values if n in card.numbers) for card in cards]
+        winnings = [sum(1 for n in card.values if n in card.numbers) for card in cards]
 
-# part 1
-answer_1 = sum(2 ** (winning - 1) for winning in winnings if winning > 0)
-print(f"answer 1 is {answer_1}")
+        # part 1
+        yield sum(2 ** (winning - 1) for winning in winnings if winning > 0)
 
-# part 2
-card2cards = {i: list(range(i + 1, i + w + 1)) for i, w in enumerate(winnings)}
-card2values = {i: 0 for i in range(len(cards))}
+        # part 2
+        card2cards = {i: list(range(i + 1, i + w + 1)) for i, w in enumerate(winnings)}
+        card2values = {i: 0 for i in range(len(cards))}
 
-for i in range(len(cards)):
-    card2values[i] += 1
-    for j in card2cards[i]:
-        card2values[j] += card2values[i]
+        for i in range(len(cards)):
+            card2values[i] += 1
+            for j in card2cards[i]:
+                card2values[j] += card2values[i]
 
-print(f"answer 2 is {sum(card2values.values())}")
+        yield sum(card2values.values())
diff --git a/src/holt59/aoc/2023/day5.py b/src/holt59/aoc/2023/day5.py
index 33d84c5..8cac8f9 100644
--- a/src/holt59/aoc/2023/day5.py
+++ b/src/holt59/aoc/2023/day5.py
@@ -1,5 +1,6 @@
-import sys
-from typing import Sequence
+from typing import Any, Iterator, Sequence
+
+from ..base import BaseSolver
 
 MAP_ORDER = [
     "seed",
@@ -12,55 +13,6 @@ MAP_ORDER = [
     "location",
 ]
 
-lines = sys.stdin.read().splitlines()
-
-# mappings from one category to another, each list contains
-# ranges stored as (source, target, length), ordered by start and
-# completed to have no "hole"
-maps: dict[tuple[str, str], list[tuple[int, int, int]]] = {}
-
-# parsing
-index = 2
-while index < len(lines):
-    p1, _, p2 = lines[index].split()[0].split("-")
-
-    # extract the existing ranges from the file - we store as (source, target, length)
-    # whereas the file is in order (target, source, length)
-    index += 1
-    values: list[tuple[int, int, int]] = []
-    while index < len(lines) and lines[index]:
-        n1, n2, n3 = lines[index].split()
-        values.append((int(n2), int(n1), int(n3)))
-        index += 1
-
-    # sort by source value
-    values.sort()
-
-    # add a 'fake' interval starting at 0 if missing
-    if values[0][0] != 0:
-        values.insert(0, (0, 0, values[0][0]))
-
-    # fill gaps between intervals
-    for i in range(len(values) - 1):
-        next_start = values[i + 1][0]
-        end = values[i][0] + values[i][2]
-        if next_start != end:
-            values.insert(
-                i + 1,
-                (end, end, next_start - end),
-            )
-
-    # add an interval covering values up to at least 2**32 at the end
-    last_start, _, last_length = values[-1]
-    values.append((last_start + last_length, last_start + last_length, 2**32))
-
-    assert all(v1[0] + v1[2] == v2[0] for v1, v2 in zip(values[:-1], values[1:]))
-    assert values[0][0] == 0
-    assert values[-1][0] + values[-1][-1] >= 2**32
-
-    maps[p1, p2] = values
-    index += 1
-
 
 def find_range(
     values: tuple[int, int], map: list[tuple[int, int, int]]
@@ -111,19 +63,71 @@ def find_range(
     return ranges
 
 
-def find_location_ranges(seeds: Sequence[tuple[int, int]]) -> Sequence[tuple[int, int]]:
-    for map1, map2 in zip(MAP_ORDER[:-1], MAP_ORDER[1:]):
-        seeds = [s2 for s1 in seeds for s2 in find_range(s1, maps[map1, map2])]
-    return seeds
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]:
+        lines = input.splitlines()
 
+        # mappings from one category to another, each list contains
+        # ranges stored as (source, target, length), ordered by start and
+        # completed to have no "hole"
+        maps: dict[tuple[str, str], list[tuple[int, int, int]]] = {}
 
-# part 1 - use find_range() with range of length 1
-seeds_p1 = [(int(s), 1) for s in lines[0].split(":")[1].strip().split()]
-answer_1 = min(start for start, _ in find_location_ranges(seeds_p1))
-print(f"answer 1 is {answer_1}")
+        def find_location_ranges(
+            seeds: Sequence[tuple[int, int]],
+        ) -> Sequence[tuple[int, int]]:
+            for map1, map2 in zip(MAP_ORDER[:-1], MAP_ORDER[1:]):
+                seeds = [s2 for s1 in seeds for s2 in find_range(s1, maps[map1, map2])]
+            return seeds
 
-# # part 2
-parts = lines[0].split(":")[1].strip().split()
-seeds_p2 = [(int(s), int(e)) for s, e in zip(parts[::2], parts[1::2])]
-answer_2 = min(start for start, _ in find_location_ranges(seeds_p2))
-print(f"answer 2 is {answer_2}")
+        # parsing
+        index = 2
+        while index < len(lines):
+            p1, _, p2 = lines[index].split()[0].split("-")
+
+            # extract the existing ranges from the file - we store as (source, target, length)
+            # whereas the file is in order (target, source, length)
+            index += 1
+            values: list[tuple[int, int, int]] = []
+            while index < len(lines) and lines[index]:
+                n1, n2, n3 = lines[index].split()
+                values.append((int(n2), int(n1), int(n3)))
+                index += 1
+
+            # sort by source value
+            values.sort()
+
+            # add a 'fake' interval starting at 0 if missing
+            if values[0][0] != 0:
+                values.insert(0, (0, 0, values[0][0]))
+
+            # fill gaps between intervals
+            for i in range(len(values) - 1):
+                next_start = values[i + 1][0]
+                end = values[i][0] + values[i][2]
+                if next_start != end:
+                    values.insert(
+                        i + 1,
+                        (end, end, next_start - end),
+                    )
+
+            # add an interval covering values up to at least 2**32 at the end
+            last_start, _, last_length = values[-1]
+            values.append((last_start + last_length, last_start + last_length, 2**32))
+
+            assert all(
+                v1[0] + v1[2] == v2[0] for v1, v2 in zip(values[:-1], values[1:])
+            )
+            assert values[0][0] == 0
+            assert values[-1][0] + values[-1][-1] >= 2**32
+
+            maps[p1, p2] = values
+            index += 1
+
+        # part 1 - use find_range() with range of length 1
+        seeds_p1 = [(int(s), 1) for s in lines[0].split(":")[1].strip().split()]
+        yield min(start for start, _ in find_location_ranges(seeds_p1))
+
+        # # part 2
+        parts = lines[0].split(":")[1].strip().split()
+        seeds_p2 = [(int(s), int(e)) for s, e in zip(parts[::2], parts[1::2])]
+        yield min(start for start, _ in find_location_ranges(seeds_p2))
diff --git a/src/holt59/aoc/2024/day1.py b/src/holt59/aoc/2024/day1.py
index acbf0c2..181e2a7 100644
--- a/src/holt59/aoc/2024/day1.py
+++ b/src/holt59/aoc/2024/day1.py
@@ -1,14 +1,17 @@
-import sys
 from collections import Counter
+from typing import Any, Iterator
 
-values = list(map(int, sys.stdin.read().strip().split()))
+from ..base import BaseSolver
 
-column_1 = sorted(values[::2])
-column_2 = sorted(values[1::2])
-counter_2 = Counter(column_2)
 
-answer_1 = sum(abs(v1 - v2) for v1, v2 in zip(column_1, column_2, strict=True))
-answer_2 = sum(value * counter_2.get(value, 0) for value in column_1)
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]:
+        values = list(map(int, input.split()))
 
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+        column_1 = sorted(values[::2])
+        column_2 = sorted(values[1::2])
+
+        yield sum(abs(v1 - v2) for v1, v2 in zip(column_1, column_2, strict=True))
+
+        counter_2 = Counter(column_2)
+        yield sum(value * counter_2.get(value, 0) for value in column_1)
diff --git a/src/holt59/aoc/2024/day10.py b/src/holt59/aoc/2024/day10.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day10.py
+++ b/src/holt59/aoc/2024/day10.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day11.py b/src/holt59/aoc/2024/day11.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day11.py
+++ b/src/holt59/aoc/2024/day11.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day12.py b/src/holt59/aoc/2024/day12.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day12.py
+++ b/src/holt59/aoc/2024/day12.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day13.py b/src/holt59/aoc/2024/day13.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day13.py
+++ b/src/holt59/aoc/2024/day13.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day14.py b/src/holt59/aoc/2024/day14.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day14.py
+++ b/src/holt59/aoc/2024/day14.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day15.py b/src/holt59/aoc/2024/day15.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day15.py
+++ b/src/holt59/aoc/2024/day15.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day16.py b/src/holt59/aoc/2024/day16.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day16.py
+++ b/src/holt59/aoc/2024/day16.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day17.py b/src/holt59/aoc/2024/day17.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day17.py
+++ b/src/holt59/aoc/2024/day17.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day18.py b/src/holt59/aoc/2024/day18.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day18.py
+++ b/src/holt59/aoc/2024/day18.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day19.py b/src/holt59/aoc/2024/day19.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day19.py
+++ b/src/holt59/aoc/2024/day19.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day2.py b/src/holt59/aoc/2024/day2.py
index 1425d49..ff59110 100644
--- a/src/holt59/aoc/2024/day2.py
+++ b/src/holt59/aoc/2024/day2.py
@@ -1,22 +1,23 @@
-import sys
+from typing import Any, Iterator
+
+from ..base import BaseSolver
 
 
-def is_safe(level: list[int]) -> bool:
-    diff = [a - b for a, b in zip(level[:-1], level[1:], strict=True)]
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]:
+        def is_safe(level: list[int]) -> bool:
+            diff = [a - b for a, b in zip(level[:-1], level[1:], strict=True)]
 
-    return sum(d > 0 for d in diff) in (0, len(diff)) and all(
-        1 <= abs(d) <= 3 for d in diff
-    )
+            return sum(d > 0 for d in diff) in (0, len(diff)) and all(
+                1 <= abs(d) <= 3 for d in diff
+            )
 
+        def is_any_safe(level: list[int]) -> bool:
+            return any(
+                is_safe(level[:i] + level[i + 1 :]) for i in range(0, len(level))
+            )
 
-def is_any_safe(level: list[int]) -> bool:
-    return any(is_safe(level[:i] + level[i + 1 :]) for i in range(0, len(level)))
+        levels = [[int(c) for c in r.split()] for r in input.splitlines()]
 
-
-levels = [[int(c) for c in r.split()] for r in sys.stdin.read().strip().splitlines()]
-
-answer_1 = sum(is_safe(level) for level in levels)
-answer_2 = sum(is_safe(level) or is_any_safe(level) for level in levels)
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+        yield sum(is_safe(level) for level in levels)
+        yield sum(is_safe(level) or is_any_safe(level) for level in levels)
diff --git a/src/holt59/aoc/2024/day20.py b/src/holt59/aoc/2024/day20.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day20.py
+++ b/src/holt59/aoc/2024/day20.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day21.py b/src/holt59/aoc/2024/day21.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day21.py
+++ b/src/holt59/aoc/2024/day21.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day22.py b/src/holt59/aoc/2024/day22.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day22.py
+++ b/src/holt59/aoc/2024/day22.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day23.py b/src/holt59/aoc/2024/day23.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day23.py
+++ b/src/holt59/aoc/2024/day23.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day24.py b/src/holt59/aoc/2024/day24.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day24.py
+++ b/src/holt59/aoc/2024/day24.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day25.py b/src/holt59/aoc/2024/day25.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day25.py
+++ b/src/holt59/aoc/2024/day25.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day3.py b/src/holt59/aoc/2024/day3.py
index 09afee0..ce2fc61 100644
--- a/src/holt59/aoc/2024/day3.py
+++ b/src/holt59/aoc/2024/day3.py
@@ -1,34 +1,30 @@
 import re
-import sys
-from typing import Iterator
+from typing import Any, Iterator
+
+from ..base import BaseSolver
 
 
-def extract_multiply(line: str) -> Iterator[int]:
-    for m in re.finditer(r"mul\(([0-9]{1,3}),\s*([0-9]{1,3})\)", line):
-        yield int(m.group(1)) * int(m.group(2))
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]:
+        def extract_multiply(line: str) -> Iterator[int]:
+            for m in re.finditer(r"mul\(([0-9]{1,3}),\s*([0-9]{1,3})\)", line):
+                yield int(m.group(1)) * int(m.group(2))
 
+        def valid_memory_blocks(line: str) -> Iterator[str]:
+            accumulate = True
+            while line:
+                if accumulate:
+                    if (dont_i := line.find("don't()")) != -1:
+                        yield line[:dont_i]
+                        line, accumulate = line[dont_i:], False
+                    else:
+                        yield line
+                        line = ""
+                else:
+                    if (do_i := line.find("do()")) != -1:
+                        line, accumulate = line[do_i:], True
+                    else:
+                        line = ""
 
-def valid_memory_blocks(line: str) -> Iterator[str]:
-    accumulate = True
-    while line:
-        if accumulate:
-            if (dont_i := line.find("don't()")) != -1:
-                yield line[:dont_i]
-                line, accumulate = line[dont_i:], False
-            else:
-                yield line
-                line = ""
-        else:
-            if (do_i := line.find("do()")) != -1:
-                line, accumulate = line[do_i:], True
-            else:
-                line = ""
-
-
-line = sys.stdin.read().strip()
-
-answer_1 = sum(extract_multiply(line))
-answer_2 = sum(sum(extract_multiply(block)) for block in valid_memory_blocks(line))
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+        yield sum(extract_multiply(input))
+        yield sum(sum(extract_multiply(block)) for block in valid_memory_blocks(input))
diff --git a/src/holt59/aoc/2024/day4.py b/src/holt59/aoc/2024/day4.py
index 656ed2e..56cd80b 100644
--- a/src/holt59/aoc/2024/day4.py
+++ b/src/holt59/aoc/2024/day4.py
@@ -1,31 +1,37 @@
 import itertools as it
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().strip().splitlines()
-n = len(lines)
+from ..base import BaseSolver
 
-answer_1 = sum(
-    line.count("XMAS") + line.count("SAMX")
-    for i in range(n)
-    for ri, rk, ro, ci, ck, cm in (
-        (1, 0, 0, 0, 1, n),
-        (0, 1, 0, 1, 0, n),
-        (0, 1, 0, 1, 1, n - i),
-        (0, -1, -1, 1, 1, n - i),
-        (1, 1, 0, 0, 1, n - i if i != 0 else 0),
-        (-1, -1, -1, 0, 1, n - i if i != 0 else 0),
-    )
-    if (
-        line := "".join(lines[ri * i + rk * k + ro][ci * i + ck * k] for k in range(cm))
-    )
-)
 
-answer_2 = sum(
-    lines[i][j] == "A"
-    and "".join(lines[i + di][j + dj] for di, dj in it.product((-1, 1), (-1, 1)))
-    in {"MSMS", "SSMM", "MMSS", "SMSM"}
-    for i, j in it.product(range(1, n - 1), range(1, n - 1))
-)
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]:
+        lines = input.splitlines()
+        n = len(lines)
 
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+        yield sum(
+            line.count("XMAS") + line.count("SAMX")
+            for i in range(n)
+            for ri, rk, ro, ci, ck, cm in (
+                (1, 0, 0, 0, 1, n),
+                (0, 1, 0, 1, 0, n),
+                (0, 1, 0, 1, 1, n - i),
+                (0, -1, -1, 1, 1, n - i),
+                (1, 1, 0, 0, 1, n - i if i != 0 else 0),
+                (-1, -1, -1, 0, 1, n - i if i != 0 else 0),
+            )
+            if (
+                line := "".join(
+                    lines[ri * i + rk * k + ro][ci * i + ck * k] for k in range(cm)
+                )
+            )
+        )
+
+        yield sum(
+            lines[i][j] == "A"
+            and "".join(
+                lines[i + di][j + dj] for di, dj in it.product((-1, 1), (-1, 1))
+            )
+            in {"MSMS", "SSMM", "MMSS", "SMSM"}
+            for i, j in it.product(range(1, n - 1), range(1, n - 1))
+        )
diff --git a/src/holt59/aoc/2024/day7.py b/src/holt59/aoc/2024/day7.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day7.py
+++ b/src/holt59/aoc/2024/day7.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day8.py b/src/holt59/aoc/2024/day8.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day8.py
+++ b/src/holt59/aoc/2024/day8.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/2024/day9.py b/src/holt59/aoc/2024/day9.py
index 4022929..07e201e 100644
--- a/src/holt59/aoc/2024/day9.py
+++ b/src/holt59/aoc/2024/day9.py
@@ -1,10 +1,7 @@
-import sys
+from typing import Any, Iterator
 
-lines = sys.stdin.read().splitlines()
+from ..base import BaseSolver
 
-answer_1 = ...
 
-answer_2 = ...
-
-print(f"answer 1 is {answer_1}")
-print(f"answer 2 is {answer_2}")
+class Solver(BaseSolver):
+    def solve(self, input: str) -> Iterator[Any]: ...
diff --git a/src/holt59/aoc/__main__.py b/src/holt59/aoc/__main__.py
index 88ddc40..59b0b11 100644
--- a/src/holt59/aoc/__main__.py
+++ b/src/holt59/aoc/__main__.py
@@ -1,9 +1,11 @@
 import argparse
 import importlib
-import os
+import logging
 import sys
 from pathlib import Path
 
+from .base import BaseSolver
+
 
 def main():
     parser = argparse.ArgumentParser("Holt59 Advent-Of-Code Runner")
@@ -40,8 +42,7 @@ def main():
     day: int = args.day
 
     # TODO: change this
-    if verbose:
-        os.environ["AOC_VERBOSE"] = "True"
+    logging.basicConfig(level=logging.INFO if verbose else logging.WARNING)
 
     if input_path is None:
         input_path = Path(__file__).parent.joinpath(
@@ -49,11 +50,18 @@ def main():
         )
     assert input_path.exists(), f"{input_path} missing"
 
+    solver_class: type[BaseSolver] = importlib.import_module(
+        f".{year}.day{day}", __package__
+    ).Solver
+
+    solver = solver_class(logging.getLogger("AOC"), year, day)
+
+    data: str
     if stdin:
-        importlib.import_module(f".{year}.day{day}", __package__)
+        data = sys.stdin.read()
     else:
         with open(input_path) as fp:
-            sys.stdin = fp
-            importlib.import_module(f".{year}.day{day}", __package__)
+            data = fp.read()
 
-        sys.stdin = sys.__stdin__
+    for i_answer, answer in enumerate(solver.solve(data.strip())):
+        print(f"answer {i_answer + 1} is {answer}")
diff --git a/src/holt59/aoc/base.py b/src/holt59/aoc/base.py
new file mode 100644
index 0000000..9ff1a16
--- /dev/null
+++ b/src/holt59/aoc/base.py
@@ -0,0 +1,13 @@
+from abc import abstractmethod
+from logging import Logger
+from typing import Any, Final, Iterator
+
+
+class BaseSolver:
+    def __init__(self, logger: Logger, year: int, day: int):
+        self.logger: Final = logger
+        self.year: Final = year
+        self.day: Final = day
+
+    @abstractmethod
+    def solve(self, input: str) -> Iterator[Any]: ...