adventofcode/2020/Day06.cs

using System;
using static System.Console;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Xunit;

namespace AdventOfCode {

  public class Day06 {

    static int CountAnswers1(string[] input) {
      int total = 0;
      var groupAnswers = new HashSet<char>();
      foreach (string line in input) {
        if (line == "") {
          total += groupAnswers.Count();
          groupAnswers.Clear();
          continue;
        }
        foreach (char c in line) {
          groupAnswers.Add(c);
        }
      }
      total += groupAnswers.Count();
      return total;
    }

    static int CountAnswers2(string[] input) {
      int total = 0;
      var groupAnswers = new HashSet<char>();
      int groupSize = 0;
      foreach (string line in input) {
        if (line == "") {
          total += groupAnswers.Count();
          groupAnswers.Clear();
          groupSize = 0;
          continue;
        }
        groupSize++;
        if (groupSize == 1) {
          foreach (char c in line) {
            groupAnswers.Add(c);
          }
        } else {
          foreach (char c in groupAnswers) {
            if (!line.Contains(c)) {
              groupAnswers.Remove(c);
            }
          }
        }
      }
      total += groupAnswers.Count();
      return total;
    }

    static int Part1() {
      string[] input = File.ReadAllLines(Util.RootDir + "day06.txt");
      return CountAnswers1(input);
    }

    static int Part2() {
      string[] input = File.ReadAllLines(Util.RootDir + "day06.txt");
      return CountAnswers2(input);
    }

    [Fact]
    public static void Test() {
      string[] example =
@"abc

a
b
c

ab
ac

a
a
a
a

b".Split('\n');
      Assert.Equal(11, CountAnswers1(example));
      Assert.Equal(6, CountAnswers2(example));

      Assert.Equal(6947, Part1());
      Assert.Equal(3398, Part2());
    }
  }
}