AoC 2024 day 10 part 2

aoc2024/src/day10/python/solution.py

@@ -13,11 +13,13 @@
 # limitations under the License.
 from typing import Sequence
 
-type Pos = tuple[int, int]
+type Pos = tuple[int, int]  # (y,x)
 
 _TRAILHEAD = 0
 _SUMMIT = 9
 _IS_GRADUAL_SLOPE = lambda level, next_level: next_level == level + 1
+_IS_WITHIN_BOUNDS = lambda pos, width, height: 0 <= pos[0] < height and 0 <= pos[1] < width
+_DIRECTIONS = ((-1, 0), (0, 1), (1, 0), (0, -1))
 
 
 def _find_trailheads(topographic_map: Sequence[str]) -> tuple[Pos, ...]:
@@ -30,28 +32,54 @@ def _find_trailheads(topographic_map: Sequence[str]) -> tuple[Pos, ...]:
   return tuple(trailhead_positions)
 
 
-def _count_reachable_summits(topo_map: Sequence[str], curr_pos: Pos, visited: set[Pos], num_summits: list[int]):
+def _count_summits(topo_map: Sequence[str], curr_pos: Pos, visited: set[Pos], counter: list[int]):
+  """Counts the number of summits that can be reached from a position."""
   curr_level = int(topo_map[curr_pos[0]][curr_pos[1]])
-  if curr_level == _SUMMIT and curr_pos not in visited:
-    num_summits[0] += 1
-    visited.add(curr_pos)
+  if curr_level == _SUMMIT:
+    if curr_pos not in visited:
+      counter[0] += 1
+      visited.add(curr_pos)
     return
   visited.add(curr_pos)
-  for step in ((-1, 0), (0, 1), (1, 0), (0, -1)):
+  for step in _DIRECTIONS:
     next_pos = (curr_pos[0] + step[0]), (curr_pos[1] + step[1])
-    within_map = 0 <= next_pos[0] < len(topo_map) and 0 <= next_pos[1] < len(topo_map[0])
-    if next_pos not in visited and within_map:
+    if next_pos not in visited and _IS_WITHIN_BOUNDS(next_pos, len(topo_map[0]), len(topo_map)):
       next_level = int(topo_map[next_pos[0]][next_pos[1]])
       if _IS_GRADUAL_SLOPE(curr_level, next_level):
-        _count_reachable_summits(topo_map, next_pos, visited, num_summits)
+        _count_summits(topo_map, next_pos, visited, counter)
+
+
+def _count_distinct_paths(topo_map: Sequence[str], curr_pos: Pos, counter: list[int]):
+  """Counts the number of distinct paths from trailhead to summit."""
+  curr_level = int(topo_map[curr_pos[0]][curr_pos[1]])
+  if curr_level == _SUMMIT:
+    counter[0] += 1
+    return
+  for step in _DIRECTIONS:
+    next_pos = (curr_pos[0] + step[0]), (curr_pos[1] + step[1])
+    if _IS_WITHIN_BOUNDS(next_pos, len(topo_map[0]), len(topo_map)):
+      next_level = int(topo_map[next_pos[0]][next_pos[1]])
+      if _IS_GRADUAL_SLOPE(curr_level, next_level):
+        _count_distinct_paths(topo_map, next_pos, counter)
 
 
 def get_score_sum(topographic_map: Sequence[str]) -> int:
   """Gets the sum of all the trails from all the trailheads."""
-  sum_scores = 0
+  score_sum = 0
   trailheads_positions: tuple[Pos, ...] = _find_trailheads(topographic_map)
   for trailhead_pos in trailheads_positions:
     num_summits = [0]  # Pass by reference.
-    _count_reachable_summits(topographic_map, trailhead_pos, set(), num_summits)
-    sum_scores += num_summits[0]
-  return sum_scores
+    _count_summits(topographic_map, trailhead_pos, set(), num_summits)
+    score_sum += num_summits[0]
+  return score_sum
+
+
+def get_rating_sum(topographic_map: Sequence[str]) -> int:
+  """Gets the sum of all distinct trails from all the trailheads."""
+  rating_sum = 0
+  trailheads_positions: tuple[Pos, ...] = _find_trailheads(topographic_map)
+  for trailhead_pos in trailheads_positions:
+    num_trails = [0]  # Pass by reference.
+    _count_distinct_paths(topographic_map, trailhead_pos, num_trails)
+    rating_sum += num_trails[0]
+  return rating_sum

aoc2024/test/day10/python/example5.txt

@@ -0,0 +1,7 @@
+1111801
+1143211
+1151121
+1165431
+1171141
+1187651
+1191111

aoc2024/test/day10/python/example6.txt

@@ -0,0 +1,7 @@
+1190219
+1111198
+1112117
+6543456
+7651987
+8761111
+9871111

aoc2024/test/day10/python/example7.txt

@@ -0,0 +1,6 @@
+012345
+123456
+234567
+345678
+416789
+567891

aoc2024/test/day10/python/example8.txt

@@ -0,0 +1,8 @@
+89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732

aoc2024/test/day10/python/test_solution.py

@@ -14,7 +14,7 @@
 import unittest
 
 from common.python3.AdventOfCodeTestCase import AdventOfCodeTestCase
-from aoc2024.src.day10.python.solution import get_score_sum
+from aoc2024.src.day10.python.solution import get_score_sum, get_rating_sum
 
 
 class TestDay09Solution(AdventOfCodeTestCase):
@@ -36,6 +36,21 @@ def test_part1_withExample4_getsScore(self):
   def test_part1_withPuzzleInput_getsScore(self):
     self.assertEqual(825, get_score_sum(self.input))
 
+  def test_part2_withExample_getsRating(self):
+    self.assertEqual(3, get_rating_sum(self.examples[4]))
+
+  def test_part2_withExample2_getsRating(self):
+    self.assertEqual(13, get_rating_sum(self.examples[5]))
+
+  def test_part2_withExample3_getsRating(self):
+    self.assertEqual(227, get_rating_sum(self.examples[6]))
+
+  def test_part2_withExample4_getsRating(self):
+    self.assertEqual(81, get_rating_sum(self.examples[7]))
+
+  def test_part2_withPuzzleInput_getsRating(self):
+    self.assertEqual(1805, get_rating_sum(self.input))
+
 
 if __name__ == '__main__':
   unittest.main()