adventofcode/2020/Program.cs

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

namespace AdventOfCode {

  public class Program {

    static int Day1Part1(List<int> numbers) {
      for (var i = 0; i < numbers.Count; i++) {
        for (var j = i + 1; j < numbers.Count; j++) {
          if (numbers[i] + numbers[j] == 2020) {
            return numbers[i] * numbers[j];
          }
        }
      }
      throw new ArgumentException("no pair of numbers summed to 2020");
    }

    static int Day1Part2(List<int> numbers) {
      for (var i = 0; i < numbers.Count; i++) {
        for (var j = i + 1; j < numbers.Count; j++) {
          for (var k = j + 1; k < numbers.Count; k++) {
            if (numbers[i] + numbers[j] + numbers[k] == 2020) {
              return numbers[i] * numbers[j] * numbers[k];
            }
          }
        }
      }
      throw new ArgumentException("no triple of numbers summed to 2020");
    }

    [Fact]
    static void Day1Test() {
      var emptyInput = new List<int>();
      var bogusInput = new List<int>() {
        111, 222, 333, 444, 555, 666, 777, 888, 999
      };
      var exampleInput = new List<int>() {
        1721, 979, 366, 299, 675, 1456
      };
      var testInput = new List<int>() {
        1768, 1847, 1905, 1713, 1826, 1846, 1824, 1976, 1687, 1867, 1665, 1606, 1946, 1886, 1858, 346, 1739, 1752, 1700, 1922, 1865, 1609, 1617, 1932, 1346, 1213, 1933, 834, 1598, 1191, 1979, 1756, 1216, 1820, 1792, 1537, 1341, 1390, 1709, 1458, 1808, 1885, 1679, 1977, 1869, 1614, 1938, 1622, 1868, 1844, 1969, 1822, 1510, 1994, 1337, 1883, 1519, 1766, 1554, 1825, 1828, 1972, 1380, 1878, 1345, 1469, 1794, 1898, 1805, 1911, 1913, 1910, 1318, 1862, 1921, 1753, 1823, 1896, 1316, 1381, 1430, 1962, 1958, 1702, 1923, 1993, 1789, 2002, 1788, 1970, 1955, 1887, 1870, 225, 1696, 1975, 699, 294, 1605, 1500, 1777, 1750, 1857, 1540, 1329, 1974, 1947, 1516, 1925, 1945, 350, 1669, 1775, 1536, 1871, 1917, 1249, 1971, 2009, 1585, 1986, 1701, 1832, 1754, 1195, 1697, 1941, 1919, 2006, 1667, 1816, 1765, 1631, 2003, 1861, 1000, 1791, 1786, 1843, 1939, 1951, 269, 1790, 1895, 1355, 1833, 1466, 1998, 1806, 1881, 1234, 1856, 1619, 1727, 1874, 1877, 195, 1783, 1797, 2010, 1764, 1863, 1852, 1841, 1892, 1562, 1650, 1942, 1695, 1730, 1965, 1632, 1981, 1900, 1991, 1884, 1278, 1062, 1394, 1999, 2000, 1827, 1873, 1926, 1434, 1802, 1579, 1879, 1671, 1549, 1875, 1838, 1338, 1864, 1718, 1800, 1928, 1749, 1990, 1705,
      };

      Assert.Throws<ArgumentException>(() => Day1Part1(emptyInput));
      Assert.Throws<ArgumentException>(() => Day1Part1(bogusInput));
      Assert.Equal(514579, Day1Part1(exampleInput));
      Assert.Equal(355875, Day1Part1(testInput));

      Assert.Throws<ArgumentException>(() => Day1Part2(emptyInput));
      Assert.Throws<ArgumentException>(() => Day1Part2(bogusInput));
      Assert.Equal(241861950, Day1Part2(exampleInput));
      Assert.Equal(140379120, Day1Part2(testInput));
    }

    static void Main(string[] args) {
      Day1Test();
    }
  }
}