using System;

using System.Net.Http;

using System.Collections.Generic;

using System.Linq;

​

// Get data

var response = await new HttpClient().GetStringAsync("https://tompafireadventofcode.free.beeceptor.com/day3"); 

​

var rows = response.Split(Environment.NewLine).Select(line => line.Select((val, index) => new CellValue(index, val)));

var columns = rows.SelectMany(row => row).GroupBy(x => x.Index);

​

// Step 1

​

var mostCommonPerColumn = columns.Select(GetMostCommon);

var leastCommonPerColumn = columns.Select(GetLeastCommon);

​

var gamma = GetDecimalValue(mostCommonPerColumn);

var epsilon = GetDecimalValue(leastCommonPerColumn);

​

var result = gamma * epsilon;

​

Console.WriteLine(result);

​

// Step 2

​

var oxygenValues = rows.ToList();

var co2ScrubValues = rows.ToList();

​

for (var i = 0; i < columns.Count(); i++)

{

    var mostCommon = GetMostCommon(oxygenValues.SelectMany(row => row).Where(x => x.Index == i));

    oxygenValues.RemoveAll(row => row.ElementAt(i) != mostCommon);

    var leastCommon = GetLeastCommon(co2ScrubValues.SelectMany(row => row).Where(x => x.Index == i));

    co2ScrubValues.RemoveAll(row => row.ElementAt(i) != leastCommon);

}

​

var oxygen = GetDecimalValue(oxygenValues.SelectMany(v => v));

var co2Scrub = GetDecimalValue(co2ScrubValues.SelectMany(v => v));

​

var result2 = oxygen * co2Scrub;

​

Console.WriteLine(result2);

​

int GetDecimalValue(IEnumerable<CellValue> values)

{

    return Convert.ToInt32(new string(values.Select(v => v.Value).ToArray()), 2);

}

​

CellValue GetMostCommon(IEnumerable<CellValue> values) 

{

    //return values.MaxBy(x => values.Count(y => y == x));

    return values.OrderByDescending(x => values.Count(y => y == x)).ThenByDescending(x => x.Value).First(); //To make sure 1 has precedence over 0 if equal count 

}

​

CellValue GetLeastCommon(IEnumerable<CellValue> values) 

{

    //return values.MinBy(x => values.Count(y => y == x));

    return values.OrderBy(x => values.Count(y => y == x)).ThenBy(x => x.Value).First(); //To make sure 0 has precedence over 1 if equal count 

}

​

public record struct CellValue(int Index, char Value); 

​