advent24/Advent24/Day5.cs

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();
        }
    }
}