Merge pull request #14 from MartinZikmund/feature/aoc2024-day13

MartinZikmund · Dec 13, 2024 · 2a9dd37 · 2a9dd37
2 parents 2e0d648 + 84569ee
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diff --git a/src/AdventOfCode.Puzzles/2024/13/Part1/Part1.cs b/src/AdventOfCode.Puzzles/2024/13/Part1/Part1.cs
@@ -0,0 +1,99 @@
+using AdventOfCode.Puzzles.Tools;
+
+namespace AdventOfCode.Puzzles._2024._13.Part1;
+
+public partial class Part1 : IPuzzleSolution
+{
+    public Task<string> SolveAsync(StreamReader inputReader)
+    {
+        long total = 0;
+        while (TryReadClawMachine(inputReader, out var clawMachine))
+        {
+            var price = SolveClawMachine(clawMachine);
+            if (price > 0)
+            {
+                total += price;
+            }
+        }
+
+        return Task.FromResult(total.ToString());
+    }
+
+    private long SolveClawMachine(ClawMachine clawMachine)
+    {
+        var buttonA = clawMachine.ButtonA;
+        var buttonB = clawMachine.ButtonB;
+        var prize = clawMachine.Prize;
+
+        // a*ax + b*bx = prizeX
+        // a*ay + b*by = prizeY
+        // a = (prizeX - b*bx) / ax
+        // ((prizeX - b*bx) / ax) * ay + b*by = prizeY
+        // ((prizeX / ax) - (b*bx / ax)) * ay + b*by = prizeY
+        // (prizeX / ax) * ay - (b*bx / ax) * ay + b*by = prizeY
+        // - (b * bx / ax) * ay + b * by = prizeY - (prizeX / ax) * ay
+        // b * by - (b* bx / ax) * ay = prizeY - (prizeX / ax) * ay
+        // b * (by - (bx / ax) * ay) = prizeY - (prizeX / ax) * ay
+        // b = (prizeY - (prizeX / ax) * ay) / (by - (bx / ax) * ay)
+
+        var prizeX = (double)prize.X;
+        var prizeY = (double)prize.Y;
+        var buttonAX = (double)buttonA.X;
+        var buttonAY = (double)buttonA.Y;
+        var buttonBX = (double)buttonB.X;
+        var buttonBY = (double)buttonB.Y;
+
+        long b = (long)Math.Round((prizeY - (prizeX / buttonAX) * buttonAY) / (buttonBY - (buttonBX / buttonAX) * buttonAY));
+        long a = (long)Math.Round((prizeX - b * buttonBX) / buttonAX);
+
+        var actualX = a * buttonAX + b * buttonBX;
+        var actualY = a * buttonAY + b * buttonBY;
+        if (actualX == prize.X && actualY == prize.Y && a >= 0 && b >= 0)
+        {
+            return a * 3 + b;
+        }
+
+        return -1;
+    }
+
+    private bool TryReadClawMachine(StreamReader reader, out ClawMachine clawMachine)
+    {
+        clawMachine = default;
+        var line = reader.ReadLine();
+        if (line == null)
+        {
+            return false;
+        }
+
+        if (string.IsNullOrWhiteSpace(line))
+        {
+            line = reader.ReadLine();
+        }
+
+        var buttonALine = line;
+        var buttonBLine = reader.ReadLine();
+        var prizeLine = reader.ReadLine();
+
+        var parts = buttonALine.Split(":")[1].Split(',');
+        var buttonAX = int.Parse(parts[0].Trim().Substring(2));
+        var buttonAY = int.Parse(parts[1].Trim().Substring(2));
+
+        parts = buttonBLine.Split(":")[1].Split(',');
+        var buttonBX = int.Parse(parts[0].Trim().Substring(2));
+        var buttonBY = int.Parse(parts[1].Trim().Substring(2));
+
+        parts = prizeLine.Split(":")[1].Split(',');
+        var prizeX = int.Parse(parts[0].Trim().Substring(2));
+        var prizeY = int.Parse(parts[1].Trim().Substring(2));
+
+        clawMachine = new ClawMachine(
+            (buttonAX, buttonAY),
+            (buttonBX, buttonBY),
+            (prizeX, prizeY)
+        );
+
+        return true;
+    }
+
+    public record ClawMachine(Point ButtonA, Point ButtonB, Point Prize);
+}
diff --git a/src/AdventOfCode.Puzzles/2024/13/Part2/Part2.cs b/src/AdventOfCode.Puzzles/2024/13/Part2/Part2.cs
@@ -0,0 +1,100 @@
+using System.Diagnostics;
+using AdventOfCode.Puzzles.Tools;
+
+namespace AdventOfCode.Puzzles._2024._13.Part2;
+
+public partial class Part2 : IPuzzleSolution
+{
+    public Task<string> SolveAsync(StreamReader inputReader)
+    {
+        long total = 0;
+        while (TryReadClawMachine(inputReader, out var clawMachine))
+        {
+            var price = SolveClawMachine(clawMachine);
+            if (price > 0)
+            {
+                total += price;
+            }
+        }
+
+        return Task.FromResult(total.ToString());
+    }
+
+    private long SolveClawMachine(ClawMachine clawMachine)
+    {
+        var buttonA = clawMachine.ButtonA;
+        var buttonB = clawMachine.ButtonB;
+        var prize = clawMachine.Prize;
+
+        // a*ax + b*bx = prizeX
+        // a*ay + b*by = prizeY
+        // a = (prizeX - b*bx) / ax
+        // ((prizeX - b*bx) / ax) * ay + b*by = prizeY
+        // ((prizeX / ax) - (b*bx / ax)) * ay + b*by = prizeY
+        // (prizeX / ax) * ay - (b*bx / ax) * ay + b*by = prizeY
+        // - (b * bx / ax) * ay + b * by = prizeY - (prizeX / ax) * ay
+        // b * by - (b* bx / ax) * ay = prizeY - (prizeX / ax) * ay
+        // b * (by - (bx / ax) * ay) = prizeY - (prizeX / ax) * ay
+        // b = (prizeY - (prizeX / ax) * ay) / (by - (bx / ax) * ay)
+
+        var prizeX = 10000000000000 + (double)prize.X;
+        var prizeY = 10000000000000 + (double)prize.Y;
+        var buttonAX = (double)buttonA.X;
+        var buttonAY = (double)buttonA.Y;
+        var buttonBX = (double)buttonB.X;
+        var buttonBY = (double)buttonB.Y;
+
+        long b = (long)Math.Round((prizeY - (prizeX / buttonAX) * buttonAY) / (buttonBY - (buttonBX / buttonAX) * buttonAY));
+        long a = (long)Math.Round((prizeX - b * buttonBX) / buttonAX);
+
+        var actualX = a * buttonAX + b * buttonBX;
+        var actualY = a * buttonAY + b * buttonBY;
+        if (actualX == prizeX && actualY == prizeY && a >= 0 && b >= 0)
+        {
+            return a * 3 + b;
+        }
+
+        return -1;
+    }
+
+    private bool TryReadClawMachine(StreamReader reader, out ClawMachine clawMachine)
+    {
+        clawMachine = default;
+        var line = reader.ReadLine();
+        if (line == null)
+        {
+            return false;
+        }
+
+        if (string.IsNullOrWhiteSpace(line))
+        {
+            line = reader.ReadLine();
+        }
+
+        var buttonALine = line;
+        var buttonBLine = reader.ReadLine();
+        var prizeLine = reader.ReadLine();
+
+        var parts = buttonALine.Split(":")[1].Split(',');
+        var buttonAX = int.Parse(parts[0].Trim().Substring(2));
+        var buttonAY = int.Parse(parts[1].Trim().Substring(2));
+
+        parts = buttonBLine.Split(":")[1].Split(',');
+        var buttonBX = int.Parse(parts[0].Trim().Substring(2));
+        var buttonBY = int.Parse(parts[1].Trim().Substring(2));
+
+        parts = prizeLine.Split(":")[1].Split(',');
+        var prizeX = int.Parse(parts[0].Trim().Substring(2));
+        var prizeY = int.Parse(parts[1].Trim().Substring(2));
+
+        clawMachine = new ClawMachine(
+            (buttonAX, buttonAY),
+            (buttonBX, buttonBY),
+            (prizeX, prizeY)
+        );
+
+        return true;
+    }
+
+    public record ClawMachine(Point ButtonA, Point ButtonB, Point Prize);
+}
diff --git a/src/AdventOfCode.Puzzles/2024/13/TestData.txt b/src/AdventOfCode.Puzzles/2024/13/TestData.txt
@@ -0,0 +1,15 @@
+Button A: X+94, Y+34
+Button B: X+22, Y+67
+Prize: X=8400, Y=5400
+
+Button A: X+26, Y+66
+Button B: X+67, Y+21
+Prize: X=12748, Y=12176
+
+Button A: X+17, Y+86
+Button B: X+84, Y+37
+Prize: X=7870, Y=6450
+
+Button A: X+69, Y+23
+Button B: X+27, Y+71
+Prize: X=18641, Y=10279