Day6 solution

Advent24/Day5.cs

@@ -0,0 +1,195 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection.Emit;
+using System.Text;
+using System.Threading.Tasks;
+using System.Text.RegularExpressions;
+
+namespace Advent24
+{
+    internal class Day5
+    {
+        private static void IngestRule(String rule, Dictionary<Int32, List<(Int32, Int32)>> ruleDict)
+        {
+            var ruleArray = rule.Split('|');
+            
+            var ruleArrayInt32 = Array.ConvertAll(ruleArray, System.Convert.ToInt32);
+
+            // if the ruleDict index doesn't already exists, add an empty list to it
+            ruleDict.TryAdd(ruleArrayInt32[0], new List<(int, int)>(2));
+            ruleDict[ruleArrayInt32[0]].Add((ruleArrayInt32[0], ruleArrayInt32[1]));
+
+            ruleDict.TryAdd(ruleArrayInt32[1], new List<(int, int)>(2));
+            ruleDict[ruleArrayInt32[1]].Add((ruleArrayInt32[0], ruleArrayInt32[1]));
+        }
+
+        private static void IngestPageRow(String pageRow, List<Dictionary<Int32, Int32>> pageRowDictsList)
+        {
+            var pageRowArray = pageRow.Split(',');
+
+            var pageRowArrayInt32 = Array.ConvertAll(pageRowArray, System.Convert.ToInt32);
+
+            pageRowDictsList.Add(new Dictionary<Int32, Int32>(pageRowArray.Length));
+
+            Int32 pageRowIndex = 1;
+
+            foreach (var pageInt32 in pageRowArrayInt32)
+            {
+                pageRowDictsList[pageRowDictsList.Count - 1].Add(pageInt32, pageRowIndex);
+
+                pageRowIndex++;
+            }
+        }
+
+        private static Int32 GetPageRowMiddle(Dictionary<Int32, Int32> pageRowDict)
+        {
+            var pageRowMiddleEnumerable = pageRowDict.Where(keyValuePair => keyValuePair.Value == (pageRowDict.Count + 1) / 2);
+            
+            return pageRowMiddleEnumerable.ElementAt(0).Key;
+        }
+
+        private static Boolean PageRowIsCorrect(Dictionary<Int32, Int32> pageRowDict, Dictionary<Int32, List<(Int32, Int32)>> ruleDict)
+        {
+            Boolean pageRowIsCorrect = true;
+
+            foreach(Int32 page in pageRowDict.Keys)
+            {
+                if (ruleDict.TryGetValue(page, out List<(int, int)>? rules))
+                {
+                    foreach (var rule in rules)
+                    {
+                        // check if the rule pertains to our pageRow
+                        if(pageRowDict.TryGetValue(rule.Item1, out Int32 leftHandIndex) &&
+                            pageRowDict.TryGetValue(rule.Item2, out Int32 rightHandIndex))
+                            // if rule violation detected, set pageRowIsCorrect to false
+                            // and break as we don't need to check the rest of the pageRow
+                            if (leftHandIndex >= rightHandIndex)
+                            {
+                                pageRowIsCorrect = false;
+                                break;
+                            }
+                    }
+
+                    // break out of outer foreach loop if nner foreach
+                    // was broken due to finding a rule violation
+                    if (!pageRowIsCorrect) break;
+                }
+            }
+
+            return pageRowIsCorrect;
+        }
+
+        private static Int32 GetCorrectMiddlesSum(Dictionary<Int32, List<(Int32, Int32)>> ruleDict, List<Dictionary<Int32, Int32>> pageRowDictsList)
+        {
+            Int32 correctMiddlesSum = 0;
+
+            foreach (var pageRowDict in pageRowDictsList)
+            {
+                if (PageRowIsCorrect(pageRowDict, ruleDict))
+                {
+                    correctMiddlesSum += GetPageRowMiddle(pageRowDict);
+                }
+            }
+            return correctMiddlesSum;
+        }
+
+        private static void CorrectPageRow(out Dictionary<Int32, Int32> correctedPageRowDict, Dictionary<Int32, Int32> pageRowDict, Dictionary<Int32, List<(Int32, Int32)>> ruleDict)
+        {
+            correctedPageRowDict = pageRowDict.ToDictionary();
+
+            Boolean correctionWasRequired;
+
+            do
+            {
+                correctionWasRequired = false;
+                foreach (Int32 page in pageRowDict.Keys)
+                {
+                    if (ruleDict.TryGetValue(page, out List<(int, int)>? rules))
+                    {
+                        foreach (var rule in rules)
+                        {
+                            // check if the rule pertains to our pageRow
+                            if (correctedPageRowDict.TryGetValue(rule.Item1, out Int32 leftHandIndex) &&
+                                correctedPageRowDict.TryGetValue(rule.Item2, out Int32 rightHandIndex))
+                                // if rule violation detected, swap the positions
+                                if (leftHandIndex >= rightHandIndex)
+                                {
+                                    // swap indices, i.e., swap positions
+                                    correctedPageRowDict[rule.Item1] = rightHandIndex;
+                                    correctedPageRowDict[rule.Item2] = leftHandIndex;
+
+                                    correctionWasRequired = true;
+                                }
+                        }
+                    }
+                }
+            } while(correctionWasRequired);
+        }
+
+        private static Int32 GetCorrectedMiddlesSum(Dictionary<Int32, List<(Int32, Int32)>> ruleDict, List<Dictionary<Int32, Int32>> pageRowDictsList)
+        {
+            Int32 correctMiddlesSum = 0;
+
+            foreach (var pageRowDict in pageRowDictsList)
+            {
+                if (!PageRowIsCorrect(pageRowDict, ruleDict))
+                {
+                    CorrectPageRow(out Dictionary<int, int> correctedPageRowDict, pageRowDict, ruleDict);
+                    correctMiddlesSum += GetPageRowMiddle(correctedPageRowDict);
+                }
+            }
+            return correctMiddlesSum;
+        }
+
+        public Day5()
+        {
+            String fileData = System.IO.File.ReadAllText(@"..\..\..\inputd5.txt");
+
+            var rulesAndPageRowsArray = fileData.Split('\n');
+
+            // indicates when we stop ingesting rules and start ingesting page rows
+            Boolean amIngestingRules = true;
+
+            // a dictionary to map from a page number to a rule containing that page number
+            // the rule is that p1 must appear before p2 if the Tuple is (p1, p2), i.e., 
+            // index of p1 must be less than index of p2
+            Dictionary<Int32, List<(Int32, Int32)>> ruleDict = [];
+
+            // a dictionary to map from a page number to its position in the array
+            List<Dictionary<Int32, Int32>> pageRowDictsList = [];
+
+            Int32 sumOfCorrectMiddles;
+            Int32 sumOfCorrectedMiddles;
+
+            foreach (var ruleOrPageRow in rulesAndPageRowsArray)
+            {
+                // empty line indicates end of rules and beginning of page rows
+                if (ruleOrPageRow == "")
+                {
+                    amIngestingRules = false;
+                    continue;
+                }
+
+                if(amIngestingRules)
+                {
+                    IngestRule(ruleOrPageRow, ruleDict);
+                }
+                else
+                {
+                    // am ingesting page rows now
+                    IngestPageRow(ruleOrPageRow, pageRowDictsList);
+                }
+            }
+
+            sumOfCorrectMiddles = GetCorrectMiddlesSum(ruleDict, pageRowDictsList);
+            sumOfCorrectedMiddles = GetCorrectedMiddlesSum(ruleDict, pageRowDictsList);
+
+            Console.WriteLine("sumOfCorrectMiddles = {0:d}", sumOfCorrectMiddles);
+            Console.WriteLine("sumOfCorrectedMiddles = {0:d}", sumOfCorrectedMiddles);
+
+            // to keep the console window from closing
+            Console.ReadKey();
+        }
+    }
+}

Advent24/Day6.cs

@@ -0,0 +1,257 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection.Emit;
+using System.Text;
+using System.Threading.Tasks;
+using System.Text.RegularExpressions;
+using System.IO.Compression;
+using System.Xml.Serialization;
+
+namespace Advent24
+{
+    internal class Day6
+    {
+        private static Boolean simulateGuardPath(String map, ref HashSet<Int32> visited, Int32 newObstacleLinearPosition = -1)
+        {
+            // get width of line to be able to navigate the text block in
+            // both dimensions
+            Int32 mapWidth = map.IndexOf('\n');
+
+            Int32 guardLinearPosition = 0;
+            Int32 guardDirection = 0; //1 = up, 2 = right, 3 = down, 4 = left
+
+            // counts the number of times we go forward in time without
+            Int32 numberOfIterationsWithoutNewVisits = 0;
+
+            Int32 previousNumberOfVisitedPositions = 0;
+
+            Int32 numberOfDirectionChanges = 0;
+
+            Boolean guardIsInMapBoundary = true;
+
+            Boolean wasInfiniteLoop = false;
+
+            // Find the initial position and direction of the guard
+            guardLinearPosition = map.IndexOf('^');
+
+            if (guardLinearPosition != -1) // in up direction
+            {
+                guardDirection = 1;
+                // invalid new obstacle position, so return prematurely with
+                // the assumption that it didn't lead to an infinite loop
+                if (newObstacleLinearPosition == guardLinearPosition)
+                    return false; // assumed value of wasInfiniteLoop
+            }
+            else // not in up direction
+            {
+                guardLinearPosition = map.IndexOf('>');
+                if (guardLinearPosition != -1) // in right direction
+                    guardDirection = 2;
+                else // not in up or right direction
+                {
+                    guardLinearPosition = map.IndexOf('v');
+                    if (guardLinearPosition != -1) // in down direction
+                        guardDirection = 3;
+                    else // not in up, right or down direction
+                    {
+                        guardLinearPosition = map.IndexOf('<');
+                        if (guardLinearPosition != -1) // in left direction
+                            guardDirection = 4;
+                        else // guard not found
+                        {
+                            guardDirection = -1;
+                            guardIsInMapBoundary = false;
+                        }
+                    }
+                }
+            }
+
+            // add intiial guard linear position
+            if (guardIsInMapBoundary) visited.Add(guardLinearPosition);
+
+            while (guardIsInMapBoundary)
+            {
+                // check next position of guard
+
+                // top
+                if (guardDirection == 1)
+                {
+                    // if obstacle detected
+                    if (guardLinearPosition - (mapWidth + 1) >= 0 &&
+                        (
+                            map[guardLinearPosition - (mapWidth + 1)] == '#' ||
+                            guardLinearPosition - (mapWidth + 1) == newObstacleLinearPosition
+                        ))
+                    {
+                        // turn 90 deg clockwise
+                        guardDirection = 2;
+                        numberOfDirectionChanges++;
+                    }
+                    // no obstacle detected
+                    else
+                        // go up one position
+                        guardLinearPosition -= mapWidth + 1;
+                }
+                // right
+                else if (guardDirection == 2)
+                {
+                    // if obstacle detected
+                    if (guardLinearPosition + 1 < map.Length &&
+                        (
+                            map[guardLinearPosition + 1] == '#' ||
+                            guardLinearPosition + 1 == newObstacleLinearPosition
+                        ))
+                    {
+                        // turn 90 deg clockwise
+                        guardDirection = 3;
+                        numberOfDirectionChanges++;
+                    }
+                    // no obstacle detected
+                    else
+                        // go up one position
+                        guardLinearPosition += 1;
+                }
+                // down
+                else if (guardDirection == 3)
+                {
+                    // if obstacle detected
+                    if (guardLinearPosition + (mapWidth + 1) < map.Length &&
+                        (
+                            map[guardLinearPosition + (mapWidth + 1)] == '#' ||
+                            guardLinearPosition + (mapWidth + 1) == newObstacleLinearPosition
+                        ))
+                    {
+                        // turn 90 deg clockwise
+                        guardDirection = 4;
+                        numberOfDirectionChanges++;
+                    }
+                    // no obstacle detected
+                    else
+                        // go up one position
+                        guardLinearPosition += (mapWidth + 1);
+                }
+                // left
+                else if (guardDirection == 4)
+                {
+                    // if obstacle detected
+                    if (guardLinearPosition - 1 >= 0 &&
+                        (
+                            map[guardLinearPosition - 1] == '#' ||
+                            guardLinearPosition - 1 == newObstacleLinearPosition
+                        ))
+                    {    
+                        // turn 90 deg clockwise
+                        guardDirection = 1;
+                        numberOfDirectionChanges++;
+                    }
+                    // no obstacle detected
+                    else
+                        // go up one position
+                        guardLinearPosition -= 1;
+                }
+
+                // right and left boundary check
+                if (guardLinearPosition > map.Length ||
+                    guardLinearPosition < 0 ||
+                    map[guardLinearPosition] == '\n')
+                    guardIsInMapBoundary = false;
+
+                // top and bottom boundary check
+                if (guardLinearPosition < 0 ||
+                    guardLinearPosition >= map.Length)
+                    guardIsInMapBoundary = false;
+
+                // if boundary check passes, add position to visited
+                if (guardIsInMapBoundary)
+                {
+                    previousNumberOfVisitedPositions = visited.Count;
+                    visited.Add(guardLinearPosition);
+                }
+
+                // if there is no change in the number of visited positions
+                if (previousNumberOfVisitedPositions == visited.Count)
+                {
+                    numberOfIterationsWithoutNewVisits++;
+
+                    // we've followed the whole path again, of which a good approximation is
+                    // that the number of unique visited positions plus the number of times
+                    // the direction has changes is equal to the number of iterations without new
+                    // visits - this will undercount intersections
+                    if (numberOfIterationsWithoutNewVisits > (visited.Count + numberOfDirectionChanges))
+                    {
+                        // Console.WriteLine("  numberOfIterationsWithoutNewVisits = {0:d}", numberOfIterationsWithoutNewVisits);
+                        wasInfiniteLoop = true;
+                        break;
+                    }
+                }
+            }
+
+            return wasInfiniteLoop;
+        }
+        public Day6()
+        {
+            String fileData = System.IO.File.ReadAllText(@"..\..\..\inputd6.txt");
+
+            
+            // set of visited linearPositions
+            HashSet<Int32> visited = [];
+
+            simulateGuardPath(fileData, ref visited);
+
+            Int32 numberOfDistinctPositions = visited.Count;
+
+            Console.WriteLine("numberOfDistinctPositions = {0:d}", numberOfDistinctPositions);
+
+            Int32 numberOfViableNewObstaclePositions = 0;
+
+            Boolean wasInfiniteLoop;
+
+            // a set of unchecked linearPositions
+            HashSet<Int32> uncheckedLinearPositions = [.. visited];
+
+            // a set of alreaedy-checked linearPositions
+            HashSet<Int32> checkedLinearPositions = [];
+
+            Int32 previousUncheckedLinearPositionsCount = uncheckedLinearPositions.Count;
+
+            // while there are unchecked visited positions
+            while (uncheckedLinearPositions.Count > 0)
+            {
+                // clear visited hashset for a fresh start per iteration
+                visited.Clear();
+
+                // get first non-checked linear position
+                var firstNonCheckedLinearPosition = uncheckedLinearPositions.First();
+
+                wasInfiniteLoop = simulateGuardPath(fileData, ref visited, firstNonCheckedLinearPosition);
+
+                // if the guard is in a loop, we have a viable obstacle position
+                if (wasInfiniteLoop)
+                    numberOfViableNewObstaclePositions++;
+
+                // update checkedLinearPositions
+                checkedLinearPositions.Add(firstNonCheckedLinearPosition);
+
+                // remove already-checked linear positions from visited
+                // so it only has new positions to add to our uncheckedLinearPositions
+                visited.ExceptWith(checkedLinearPositions);
+
+                previousUncheckedLinearPositionsCount = uncheckedLinearPositions.Count;
+
+                // update uncheckedLinearPositions to remove firstNonCheckedLinearPosition
+                // and add newly visisted linear positions
+                uncheckedLinearPositions.Remove(firstNonCheckedLinearPosition);
+                uncheckedLinearPositions.UnionWith(visited);
+
+             // if (uncheckedLinearPositions.Count > previousUncheckedLinearPositionsCount)
+             //     Console.WriteLine("(change) uncheckedLinearPositions.Count = {0:d}", uncheckedLinearPositions.Count - previousUncheckedLinearPositionsCount);
+            }
+
+            Console.WriteLine("numberOfViableNewObstaclePositions = {0:d}", numberOfViableNewObstaclePositions);
+
+            // to keep the console window from closing
+            Console.ReadKey();
+        }
+    }
+}

Advent24/Program.cs

@@ -10,7 +10,9 @@ namespace Advent24
             //_ = new Day1();
             //_ = new Day2();
             //_ = new Day3();
-            _ = new Day4();
+            //_ = new Day4();
+            // _ = new Day5();
+            _ = new Day6();
         }
     }
 }

Advent24/inputd5test.txt

@@ -0,0 +1,28 @@
+47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47

Advent24/inputd6.txt

@@ -0,0 +1,130 @@
+..........#...........#...........#.............................#......................#.........#................................
+..........................#.........#......#.................................#...........................#........................
+..................................#...#................................................................................#..........
+.#...............#.....#..........#.........#......#........#................................#......#.............................
+...#.......#.............#.............................................#.........##...............#.................#.............
+.......................................#.............#..................#........#.......#.........#...............#.........#....
+.....#..................#..#..#.........................#...................#....#........#.............................#.........
+.......#.............................#..........#......#..........................##......#.......................##..............
+.....#.....#........................................................................................#.......#.....................
+.................................#............#...#.....................................................#.........#...............
+...............#.....#..#....#....#.....................................................#............#........#.#.................
+.......#.....#...........................................................#............................#.................#....#....
+...........................#.................#....................................#...............#..#........................#...
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+.................#...............#............#.......#.#...............................................#..................#......
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+.#.......#........................................................................................................................
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+...............................#...#........#............................................#.................#......................
+......#.........................#......................#.....#.#..............#..................#.......#..................#.....
+.................#........#...#........................#.............................#............................................
+#...........................................................................#............................#................#.......
+..........................................................................#................#......................................
+.............#.............................................................................#.........................#............
+.#...........#.......#.......#.....#....#.......#........#....................#........................#........................#.
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+....#........#.##......#...#......................................................................................................
+..#..#.#.#.....................#................................#...................................#.....#...#...................
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+...................................................................................#........#.......#....#............#...........
+.....#....#..................#...............#.............................................#.#....................#...............
+.....................#..........#............#..................................#......................#.#.....#................#.
+..........#.........................................#...............#.............................................................
+.......#......................#.............#.....#..............#........................#.....#.........#.................#...#.
+..................................................................#.....#...............................................#........#
+.......#..........#.......#....#.......#..........#....#............................................#.#...........................
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+.........#..................#..................#..................................................................................
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+............#.........................#........#....#..#..................................#..................#....................
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+........................#................#..............#...##...............................#..................##....#...........
+....#.#...#.....#..................................#..............................#...........#.....................#.............
+......................#.........................................................................#..........#.............#........
+.#......#............................................................#...............................#...#........................
+.......##.....................#.....#...........#......##.......##...................#...............................#............
+...#...#........#...............#......#......#.....#...#.................................................................#.......
+..................#.......................#...............................................#.................#.............#..#....
+.....................#.......#....#...#............................#.....................#............#.....................#.....
+................................................................#....#......#............#..................#.........#...........
+.......................#...................#..............................................................................###.....
+...............................#...........#................................#........#..#....#............................#.......
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