Solution for day 18, part 2.

hainesr · Dec 22, 2024 · b2287d0 · b2287d0
1 parent 80616c4
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diff --git a/lib/aoc2024/days/ram_run.rb b/lib/aoc2024/days/ram_run.rb
@@ -39,6 +39,14 @@ def part1(steps: 1024, finish: [70, 70])
       Common::AStar.solve(@start, finish, neighbours, cost, heuristic)
     end
 
+    def part2(steps: 1024, finish: [70, 70])
+      pos = (steps...@positions.length).bsearch do |step|
+        part1(steps: step, finish: finish).nil?
+      end
+
+      @positions[pos - 1].join(',') # Array indexes start at 0!
+    end
+
     def parse_input(input)
       input.lines(chomp: true).map do |line|
         line.split(',').map(&:to_i)

diff --git a/test/days/ram_run_test.rb b/test/days/ram_run_test.rb
@@ -55,4 +55,10 @@ def test_part1
 
     assert_equal(22, @rr.part1(steps: 12, finish: [6, 6]))
   end
+
+  def test_part2
+    @rr.setup(INPUT)
+
+    assert_equal('6,1', @rr.part2(steps: 12, finish: [6, 6]))
+  end
 end