63 lines
1.6 KiB
C#
63 lines
1.6 KiB
C#
namespace aoc2021;
|
|
|
|
/// <summary>
|
|
/// Day 3: <see href="https://adventofcode.com/2021/day/3"/>
|
|
/// </summary>
|
|
public sealed class Day03 : Day
|
|
{
|
|
private readonly List<string> _report;
|
|
|
|
public Day03() : base(3, "Binary Diagnostic")
|
|
{
|
|
_report = Input.ToList();
|
|
}
|
|
|
|
public override object Part1()
|
|
{
|
|
var l = _report.Count / 2;
|
|
var g = new StringBuilder();
|
|
var e = new StringBuilder();
|
|
|
|
foreach (var i in Enumerable.Range(0, _report[0].Length))
|
|
{
|
|
var ones = _report.Select(r => r[i]).Count(c => c == '1');
|
|
g.Append(ones > l ? '1' : '0');
|
|
e.Append(ones > l ? '0' : '1');
|
|
}
|
|
|
|
var gamma = g.ToString().BigIntegerFromBinaryString();
|
|
var epsilon = e.ToString().BigIntegerFromBinaryString();
|
|
|
|
return gamma * epsilon;
|
|
}
|
|
|
|
public override object Part2()
|
|
{
|
|
var o = _report;
|
|
var c = _report;
|
|
|
|
char MostCommon(int i, IReadOnlyCollection<string> report) =>
|
|
report.Count(r => r[i] == '1') >= report.Count / 2.0 ? '1' : '0';
|
|
|
|
var i = 0;
|
|
while (o.Count > 1)
|
|
{
|
|
var most = MostCommon(i, o);
|
|
o = o.Where(r => r[i] == most).ToList();
|
|
i++;
|
|
}
|
|
var o2 = o.Single().BigIntegerFromBinaryString();
|
|
|
|
i = 0;
|
|
while (c.Count > 1)
|
|
{
|
|
var most = MostCommon(i, c);
|
|
c = c.Where(r => r[i] != most).ToList();
|
|
i++;
|
|
}
|
|
var co2 = c.Single().BigIntegerFromBinaryString();
|
|
|
|
return o2 * co2;
|
|
}
|
|
}
|