adventofcode/2020/Day02.cs

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

namespace AdventOfCode {

  public class Day02 {

    static bool IsPasswordValid1(string spec) {
      string[] tokens = spec.Split(' ');
      string[] numbers = tokens[0].Split('-');
      int min = int.Parse(numbers[0]);
      int max = int.Parse(numbers[1]);
      char required = tokens[1][0];
      string password = tokens[2];

      int count = 0;
      for (int i = 0; i < password.Length; i++) {
        if (password[i] == required) {
          count++;
        }
      }
      return min <= count && count <= max;
    }

    static bool IsPasswordValid2(string spec) {
      string[] tokens = spec.Split(' ');
      string[] numbers = tokens[0].Split('-');
      int lowIndex = int.Parse(numbers[0]) - 1;
      int highIndex = int.Parse(numbers[1]) - 1;
      char required = tokens[1][0];
      string password = tokens[2];
      return
        (password[lowIndex] == required && password[highIndex] != required) ||
        (password[lowIndex] != required && password[highIndex] == required);
    }

    static int Part1() {
      return File.ReadAllLines(Util.RootDir + "day02.txt").Count(IsPasswordValid1);
    }

    static int Part2() {
      return File.ReadAllLines(Util.RootDir + "day02.txt").Count(IsPasswordValid2);
    }

    [Fact]
    public static void Test() {
      Assert.True(IsPasswordValid1("1-3 a: abcde"));
      Assert.False(IsPasswordValid1("1-3 b: cdefg"));
      Assert.True(IsPasswordValid1("2-9 c: ccccccccc"));
      Assert.Equal(603, Part1());

      Assert.True(IsPasswordValid2("1-3 a: abcde"));
      Assert.False(IsPasswordValid2("1-3 b: cdefg"));
      Assert.False(IsPasswordValid2("2-9 c: ccccccccc"));
      Assert.Equal(404, Part2());
    }
  }
}