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2019 Day 03 solution
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Josh Creek
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using System;
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using System.IO;
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using System.Collections.Generic;
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using System.Linq;
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namespace Day_03
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{
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class Program
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{
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static void Main(string[] args)
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{
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//Part1();
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Part2();
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}
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public class WireTouchPoint
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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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}
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static List<WireTouchPoint> FindAllWireTouchPoints(List<string> wireCommands)
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{
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List<WireTouchPoint> touchPoints = new List<WireTouchPoint>(){};
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int currentX = 0;
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int currentY = 0;
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WireTouchPoint initialWTP = new WireTouchPoint();
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initialWTP.x = currentX;
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initialWTP.y = currentY;
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touchPoints.Add(initialWTP);
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// For each command, record every co-ordinate the wire touches
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foreach(string wireCommand in wireCommands)
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{
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// Not bothering with error catching for converting strings to ints as the data cannot be wrongly typed in the input file
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int distance = System.Convert.ToInt32(wireCommand.Substring(1));
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// Handle the different commands in the first letter of each command string
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switch (wireCommand[0])
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{
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case 'U':
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// Up
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for(int i = 0; i < distance; i++)
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{
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currentY += 1;
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WireTouchPoint wtp = new WireTouchPoint();
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wtp.x = currentX;
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wtp.y = currentY;
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touchPoints.Add(wtp);
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}
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break;
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case 'D':
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// Down
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for(int i = 0; i < distance; i++)
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{
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currentY -= 1;
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WireTouchPoint wtp = new WireTouchPoint();
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wtp.x = currentX;
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wtp.y = currentY;
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touchPoints.Add(wtp);
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}
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break;
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case 'L':
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// Left
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for(int i = 0; i < distance; i++)
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{
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currentX -= 1;
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WireTouchPoint wtp = new WireTouchPoint();
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wtp.x = currentX;
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wtp.y = currentY;
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touchPoints.Add(wtp);
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}
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break;
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case 'R':
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// Right
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for(int i = 0; i < distance; i++)
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{
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currentX += 1;
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WireTouchPoint wtp = new WireTouchPoint();
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wtp.x = currentX;
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wtp.y = currentY;
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touchPoints.Add(wtp);
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}
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break;
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default:
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break;
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}
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}
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return touchPoints;
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}
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internal class WireTouchPointComparer : IEqualityComparer<WireTouchPoint>
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{
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public bool Equals(WireTouchPoint wtp1, WireTouchPoint wtp2)
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{
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if(wtp1.x == wtp2.x && wtp1.y == wtp2.y)
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{
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return true;
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}
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return false;
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}
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// public int GetHashCode(WireTouchPoint obj)
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// {
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// return obj.x.GetHashCode();
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// }
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public int GetHashCode(WireTouchPoint obj)
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{
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unchecked
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{
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int hash = 17;
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hash = hash * 23 + obj.x.GetHashCode();
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hash = hash * 23 + obj.y.GetHashCode();
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return hash;
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}
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}
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}
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static void Part1()
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{
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// Each line is one wire's path trace
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var wire1 = File.ReadAllLines("input.txt")[0];
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var wire2 = File.ReadAllLines("input.txt")[1];
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List<string> wire1Commands = wire1.Split(',').ToList();
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List<string> wire2Commands = wire2.Split(',').ToList();
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// Find all points each wire touches
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List<WireTouchPoint> wire1TouchPoints = FindAllWireTouchPoints(wire1Commands);
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List<WireTouchPoint> wire2TouchPoints = FindAllWireTouchPoints(wire2Commands);
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// Find all points where the two wires cross
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var crossingPoints = wire1TouchPoints.Intersect(wire2TouchPoints, new WireTouchPointComparer()).Where(cp => cp.x != 0 && cp.y != 0);
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// Declare a large default shortest distance, probably should be setting as null and null-checking later but multitasking while writing this so cba
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int shortestManhattanDistance = 9999999;
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// For each crossing point, work out the Manhattan distance to the central port
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foreach(WireTouchPoint crossingPoint in crossingPoints)
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{
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// Convert co-ordinates to be positive numbers for calculating distance
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int xVal = crossingPoint.x > 0 ? crossingPoint.x : crossingPoint.x * -1;
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int yVal = crossingPoint.y > 0 ? crossingPoint.y : crossingPoint.y * -1;
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int manhattanDistance = (xVal - 0) + (yVal - 0);
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// Work out if it is shorter than the previously found one
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if(manhattanDistance < shortestManhattanDistance)
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{
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shortestManhattanDistance = manhattanDistance;
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}
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}
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Console.WriteLine("Part 1: The Manhattan distance from the central port to the closest intersection is " + shortestManhattanDistance);
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}
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static void Part2()
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{
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// Each line is one wire's path trace
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var wire1 = File.ReadAllLines("input.txt")[0];
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var wire2 = File.ReadAllLines("input.txt")[1];
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List<string> wire1Commands = wire1.Split(',').ToList();
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List<string> wire2Commands = wire2.Split(',').ToList();
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// Find all points each wire touches
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List<WireTouchPoint> wire1TouchPoints = FindAllWireTouchPoints(wire1Commands);
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List<WireTouchPoint> wire2TouchPoints = FindAllWireTouchPoints(wire2Commands);
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// Find all points where the two wires cross
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var crossingPoints = wire1TouchPoints.Intersect(wire2TouchPoints, new WireTouchPointComparer()).Where(cp => cp.x != 0 && cp.y != 0);
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// Declare a large default minimum steps, probably should be setting as null and null-checking later but multitasking while writing this so cba
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int minimumSteps = 9999999;
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foreach(WireTouchPoint crossingPoint in crossingPoints)
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{
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// Calculate the number of steps each wire takes to reach each the intersection
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// If a wire visits a position on the grid multiple times, use the steps value from the first time it visits that position when calculating the total value of a specific intersection.
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// The number of steps a wire takes is the total number of grid squares the wire has entered to get to that location, including the intersection being considered.
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// Calculate the minimum number of steps each wire takes to reach the crossing point (using the index rather than index + 1 as the lists are zero-indexed ordered by the route taken but we want to ignore the start co-ordinates) - this will always return the first (i.e. closest) index
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int steps1 = wire1TouchPoints.FindIndex(tp => tp.x == crossingPoint.x && tp.y == crossingPoint.y);
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int steps2 = wire2TouchPoints.FindIndex(tp => tp.x == crossingPoint.x && tp.y == crossingPoint.y);
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int totalSteps = steps1 + steps2;
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// Work out if it is fewer steps than the previously found one
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if(totalSteps < minimumSteps)
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{
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minimumSteps = totalSteps;
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}
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}
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Console.WriteLine("Part 2: The fewest combined steps the wires must take to reach an intersection is " + minimumSteps);
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}
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}
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}
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