109 lines
3.5 KiB
C#
109 lines
3.5 KiB
C#
using System;
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namespace AOC2017
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{
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class BScottDay3 : BScottSolution
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{
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public override string Name => "Day 3: Spiral Memory";
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public override void Run()
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{
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Console.WriteLine($"Part 1 Example Answer #1 (1): {SpiralMemoryPart1(1)}");
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Console.WriteLine($"Part 1 Example Answer #2 (12): {SpiralMemoryPart1(12)}");
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Console.WriteLine($"Part 1 Example Answer #3 (23): {SpiralMemoryPart1(23)}");
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Console.WriteLine($"Part 1 Example Answer #4 (1024): {SpiralMemoryPart1(1024)}");
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int value = 325489; // Puzzle Input
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Console.WriteLine($"Part 1 Answer: {SpiralMemoryPart1(value)}");
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Console.WriteLine($"Part 2 Answer: {SpiralMemoryPart2(value)}");
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}
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static int SpiralMemoryPart1(int value)
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{
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Point position = GetPosition(value);
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return Math.Abs(position.X) + Math.Abs(position.Y);
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}
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// Unfortunatly I can't take credit for solving this. This was ported and optimized slightly from a C function posted to github.
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// Included this just for the sake of completion.
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// Source: https://github.com/vesche/adventofcode-2017/blob/master/day03.c
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// Integer Sequence: https://oeis.org/A141481/b141481.txt
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static int SpiralMemoryPart2(int value)
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{
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int x = 0, y = 0, dx = 0, dy = -1;
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int[,] array = new int[1000, 3];
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int[,] coords = new int[,] { { 1, 0 }, { 1, -1 }, { 0, -1 }, { -1, -1 }, { -1, 0 }, { -1, 1 }, { 0, 1 }, { 1, 1 } };
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for (int step = 0; step < 1000; step++)
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{
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int total = 0;
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for (int i = 0; i < 1000; i++)
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{
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int tx = array[i, 0];
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int ty = array[i, 1];
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for (int j = 0; j < 8; j++)
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{
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if ((x + coords[j, 0] == tx) && (y + coords[j, 1] == ty))
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total += array[i, 2];
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}
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}
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array[step, 0] = x;
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array[step, 1] = y;
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array[step, 2] = (x == 0 && y == 0) ? 1 : total;
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if (total > value)
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return total;
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if ((x == y) || ((x < 0) && (x == -y)) || ((x > 0) && (x == 1 - y)))
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{
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int dxtmp = dx;
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dx = -dy;
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dy = dxtmp;
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}
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x += dx;
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y += dy;
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}
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return -1;
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}
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// Inverse ulam spiral coords
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static Point GetPosition(int n)
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{
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double k = Math.Ceiling((Math.Sqrt(n) - 1) / 2);
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double t = 2 * k + 1;
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double m = Math.Pow(t, 2);
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t = t - 1;
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if (n >= m - t)
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return new Point((int)(k - (m - n)), (int)-k);
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m = m - t;
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if (n >= m - t)
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return new Point((int)-k, (int)(-k + (m - n)));
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m = m - t;
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if (n >= m - t)
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return new Point((int)(-k + (m - n)), (int)k);
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return new Point((int)k, (int)(k - (m - n - t)));
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}
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struct Point
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{
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public int X { get; set; }
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public int Y { get; set; }
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public Point(int x, int y)
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{
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this.X = x;
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this.Y = y;
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}
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}
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}
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}
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