day3big

aoc2020/Day3.cs

@@ -1,4 +1,6 @@
+using System.IO;
 using System.Linq;
+using System.Numerics;
 
 namespace aoc2020
 {
@@ -9,7 +11,7 @@ namespace aoc2020
 
         public Day3()
         {
-            _grid = Input.ToArray();
+            _grid = File.ReadLines("input/day3big.in").ToArray();
             _width = _grid[0].Length;
         }
 
@@ -32,18 +34,14 @@ namespace aoc2020
 
         public override string Part2()
         {
-            var slopes = new[]
-            {
-                (1, 1),
-                (3, 1),
-                (5, 1),
-                (7, 1),
-                (1, 2)
-            };
+            var xSlops = new[] {2, 3, 4, 5, 8, 9, 12, 16, 18, 24, 32, 36, 48, 54, 65};
+            var ySlops = new[] {1, 5, 7, 11, 13, 17, 19, 23, 25, 29, 31, 25, 37, 41, 47};
 
-            return slopes
+            return xSlops
+                .SelectMany(x => ySlops, (x, y) => (x, y))
                 .Select(s => CountSlope(s.Item1, s.Item2))
-                .Aggregate((acc, i) => acc * i)
+                .Select(s => new BigInteger(s))
+                .Aggregate(BigInteger.Multiply)
                 .ToString();
         }
     }