Day03

AdventOfCode2020.Tests/Day03_Tests.cs

@@ -0,0 +1,53 @@
+using AdventOfCode2020;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace AdventOfCode2020.Tests
+{
+    [TestClass()]
+    public class Day03_Tests
+    {
+        [TestMethod()]
+        public void ResolvePart1__Example()
+        {
+            IDay day03 = new Day03();
+
+            string result = day03.ResolvePart1(new string[] {
+                "..##.......",
+                "#...#...#..",
+                ".#....#..#.",
+                "..#.#...#.#",
+                ".#...##..#.",
+                "..#.##.....",
+                ".#.#.#....#",
+                ".#........#",
+                "#.##...#...",
+                "#...##....#",
+                ".#..#...#.#",
+            });
+
+            Assert.AreEqual("7", result);
+        }
+
+        [TestMethod()]
+        public void ResolvePart2__Example()
+        {
+            IDay day03 = new Day03();
+
+            string result = day03.ResolvePart2(new string[] {
+                "..##.......",
+                "#...#...#..",
+                ".#....#..#.",
+                "..#.#...#.#",
+                ".#...##..#.",
+                "..#.##.....",
+                ".#.#.#....#",
+                ".#........#",
+                "#.##...#...",
+                "#...##....#",
+                ".#..#...#.#",
+            });
+
+            Assert.AreEqual("336", result);
+        }
+    }
+}

AdventOfCode2020/Day03.cs

@@ -0,0 +1,117 @@
+/*
+
+--- Day 3: Toboggan Trajectory ---
+
+With the toboggan login problems resolved, you set off toward the airport. While travel by toboggan might be easy, it's certainly not safe: there's very minimal steering and the area is covered in trees. You'll need to see which angles will take you near the fewest trees.
+
+Due to the local geology, trees in this area only grow on exact integer coordinates in a grid. You make a map (your puzzle input) of the open squares (.) and trees (#) you can see. For example:
+
+..##.......
+#...#...#..
+.#....#..#.
+..#.#...#.#
+.#...##..#.
+..#.##.....
+.#.#.#....#
+.#........#
+#.##...#...
+#...##....#
+.#..#...#.#
+
+These aren't the only trees, though; due to something you read about once involving arboreal genetics and biome stability, the same pattern repeats to the right many times:
+
+..##.........##.........##.........##.........##.........##.......  --->
+#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
+.#....#..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
+..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
+.#...##..#..#...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
+..#.##.......#.##.......#.##.......#.##.......#.##.......#.##.....  --->
+.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
+.#........#.#........#.#........#.#........#.#........#.#........#
+#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...
+#...##....##...##....##...##....##...##....##...##....##...##....#
+.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#  --->
+
+You start on the open square (.) in the top-left corner and need to reach the bottom (below the bottom-most row on your map).
+
+The toboggan can only follow a few specific slopes (you opted for a cheaper model that prefers rational numbers); start by counting all the trees you would encounter for the slope right 3, down 1:
+
+From your starting position at the top-left, check the position that is right 3 and down 1. Then, check the position that is right 3 and down 1 from there, and so on until you go past the bottom of the map.
+
+The locations you'd check in the above example are marked here with O where there was an open square and X where there was a tree:
+
+..##.........##.........##.........##.........##.........##.......  --->
+#..O#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
+.#....X..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
+..#.#...#O#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
+.#...##..#..X...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
+..#.##.......#.X#.......#.##.......#.##.......#.##.......#.##.....  --->
+.#.#.#....#.#.#.#.O..#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
+.#........#.#........X.#........#.#........#.#........#.#........#
+#.##...#...#.##...#...#.X#...#...#.##...#...#.##...#...#.##...#...
+#...##....##...##....##...#X....##...##....##...##....##...##....#
+.#..#...#.#.#..#...#.#.#..#...X.#.#..#...#.#.#..#...#.#.#..#...#.#  --->
+
+In this example, traversing the map using this slope would cause you to encounter 7 trees.
+
+Starting at the top-left corner of your map and following a slope of right 3 and down 1, how many trees would you encounter?
+
+Part Two ---
+
+Time to check the rest of the slopes - you need to minimize the probability of a sudden arboreal stop, after all.
+
+Determine the number of trees you would encounter if, for each of the following slopes, you start at the top-left corner and traverse the map all the way to the bottom:
+
+    Right 1, down 1.
+    Right 3, down 1. (This is the slope you already checked.)
+    Right 5, down 1.
+    Right 7, down 1.
+    Right 1, down 2.
+
+In the above example, these slopes would find 2, 7, 3, 4, and 2 tree(s) respectively; multiplied together, these produce the answer 336.
+
+What do you get if you multiply together the number of trees encountered on each of the listed slopes?
+
+*/
+
+namespace AdventOfCode2020
+{
+    public class Day03 : IDay
+    {
+        public string ResolvePart1(string[] inputs)
+        {
+            int treeCnt = FollowSlope(inputs, 3, 1);
+            return treeCnt.ToString();
+        }
+
+        public string ResolvePart2(string[] inputs)
+        {
+            int treeCnt1 = FollowSlope(inputs, 1, 1);
+            int treeCnt2 = FollowSlope(inputs, 3, 1);
+            int treeCnt3 = FollowSlope(inputs, 5, 1);
+            int treeCnt4 = FollowSlope(inputs, 7, 1);
+            int treeCnt5 = FollowSlope(inputs, 1, 2);
+            long treeMult = treeCnt1 * treeCnt2 * treeCnt3 * treeCnt4 * treeCnt5;
+            return treeMult.ToString();
+        }
+
+        private static int FollowSlope(string[] inputs, int dx, int dy)
+        {
+            int x = 0;
+            int y = 0;
+            int treeCnt = 0;
+            x += dx;
+            y += dy;
+            while (y < inputs.Length)
+            {
+                string input = inputs[y];
+                char c = input[x % input.Length];
+                if (c == '#') { treeCnt++; }
+                x += dx;
+                y += dy;
+            }
+            return treeCnt;
+        }
+
+    }
+}

AdventOfCode2020/Program.cs

@@ -7,13 +7,14 @@ namespace AdventOfCode2020
     {
         static void Main(string[] args)
         {
-            int currentDayNumber = 2;
+            int currentDayNumber = 3;
             IDay currentDay = null;
 
             switch (currentDayNumber)
             {
                 case 1: currentDay = new Day01(); break;
                 case 2: currentDay = new Day02(); break;
+                case 3: currentDay = new Day03(); break;
             }
 
             Console.WriteLine(string.Format("Day {0:00}", currentDayNumber));

AdventOfCode2020/inputs/Day03.txt

@@ -0,0 +1,323 @@
+....#..#.................#..#..
+#..#.#.#..#.###.#..#...#..#....
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