AoC 2023 Day 1 Part 2

aoc2023/src/day01/python/solution.py

@@ -11,32 +11,93 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-def _find_first_digit(string: str) -> int:
+_SPELLED_OUT_NUMBERS = (
+  'zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine')
+_NUMBERS = tuple(str(i) for i in range(0, 10))
+
+
+def _find_first_digit(string: str, read_spelled: bool) -> int:
   """Returns the left-most digit in a string."""
-  return next(int(char) for char in string if char.isdigit())
+  if not read_spelled:
+    return next(int(char) for char in string if char.isdigit())
+
+  min_index = len(string)
+  found_index = len(string)
+  num_at_min_index = None
+  for number in _NUMBERS:
+    try:
+      found_index = string.index(number)
+    except ValueError:
+      # Number not found, ignore.
+      pass
+    if found_index < min_index:
+      num_at_min_index = int(number)
+      min_index = found_index
+  for i in range(len(_SPELLED_OUT_NUMBERS)):
+    try:
+      found_index = string.index(_SPELLED_OUT_NUMBERS[i])
+    except ValueError:
+      # Number not found, ignore.
+      pass
+    if found_index < min_index:
+      num_at_min_index = int(i)
+      min_index = found_index
+  return num_at_min_index
 
 
-def _find_last_digit(string: str) -> int:
+def _find_last_digit(string: str, read_spelled: bool) -> int:
   """Returns the right-most digit in a string."""
-  return next(
-    int(string[i]) for i in range(len(string) - 1, -1, -1)
-    if string[i].isdigit())
+  if not read_spelled:
+    return next(
+      int(string[i]) for i in range(len(string) - 1, -1, -1)
+      if string[i].isdigit())
 
+  max_index = -1
+  found_index = -1
+  num_at_max_index = None
+  for number in _NUMBERS:
+    try:
+      found_index = string.rfind(number)
+    except ValueError:
+      # Number not found, ignore.
+      pass
+    if found_index > max_index:
+      num_at_max_index = int(number)
+      max_index = found_index
+  for i in range(len(_SPELLED_OUT_NUMBERS)):
+    try:
+      found_index = string.rfind(_SPELLED_OUT_NUMBERS[i])
+    except ValueError:
+      # Number not found, ignore.
+      pass
+    if found_index > max_index:
+      num_at_max_index = int(i)
+      max_index = found_index
+  return num_at_max_index
 
-def _get_calibration_value(string: str) -> int:
+
+def _get_calibration_value(string: str,
+                           read_spelled: bool) -> int:
   """Calculates calibration value of a string."""
-  return _find_first_digit(string) * 10 + _find_last_digit(string)
+
+  return (_find_first_digit(string, read_spelled) * 10
+          + _find_last_digit(string, read_spelled))
 
 
-def sum_calibration_values(calibration_document: tuple[str, ...]) -> int:
+def sum_calibration_values(calibration_document: tuple[str, ...],
+                           read_spelled: bool = False) -> int:
   """Calculates sum of the calibration values.
 
   The calibration value can be found by combining the first digit and the last
    digit (in that order) to form a single two-digit number.
 
   Args
     calibration_document A calibration document.
+    read_spelled Whether to consider spelled out numbers in the calibration
+        document lines. False by default.
   Returns
     Sum of all calibration values in the document.
   """
-  return sum((_get_calibration_value(line) for line in calibration_document))
+  return sum(
+    (_get_calibration_value(line, read_spelled)
+     for line in calibration_document))

aoc2023/test/day01/python/example2.txt

@@ -0,0 +1,7 @@
+two1nine
+eightwothree
+abcone2threexyz
+xtwone3four
+4nineeightseven2
+zoneight234
+7pqrstsixteen

aoc2023/test/day01/python/test_solution.py

@@ -27,6 +27,15 @@ def test_part1_withExampleInput_sumsCalibrationValues(self):
   def test_part1_withInput_sumsCalibrationValues(self):
     self.assertEqual(53334, sum_calibration_values(self.input))
 
+  def test_part2_withExampleInput_sumsCalibrationValues(self):
+    self.assertEqual(281,
+                     sum_calibration_values(self.examples[1],
+                                            read_spelled=True))
+
+  def test_part2_withInput_sumsCalibrationValues(self):
+    self.assertEqual(52834,
+                     sum_calibration_values(self.input, read_spelled=True))
+
 
 if __name__ == '__main__':
   unittest.main()