From 1d583ed6e4f0534743bf0976ab214a5310345047 Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@gmail.com>
Date: Sat, 19 Nov 2022 10:30:09 -0800
Subject: [PATCH] 2020-2/3

---
 2020/02.cpp         | 71 +++++++++++++++++++++++++++++++++++++++
 2020/03.cpp         | 82 +++++++++++++++++++++++++++++++++++++++++++++
 2020/CMakeLists.txt |  7 ++--
 3 files changed, 158 insertions(+), 2 deletions(-)
 create mode 100644 2020/02.cpp
 create mode 100644 2020/03.cpp

diff --git a/2020/02.cpp b/2020/02.cpp
new file mode 100644
index 0000000..a2d5c75
--- /dev/null
+++ b/2020/02.cpp
@@ -0,0 +1,71 @@
+#include <algorithm>
+#include <cstdint>
+#include <iostream>
+#include <tuple>
+#include <cstdio>
+#include <cstdlib>
+
+#include <doctest.h>
+
+#include <aocpp/Startup.hpp>
+
+namespace {
+
+using Entry = std::tuple<std::size_t, std::size_t, char, std::string>;
+
+auto Parse(std::string const& str) -> Entry
+{
+  std::size_t lo, hi, n;
+  char letter;
+  auto res = std::sscanf(str.c_str(), "%zu-%zu %c: %zn", &lo, &hi, &letter, &n);
+  if (res != 3) { throw std::runtime_error{"bad input"}; }
+  return {lo, hi, letter, str.substr(n)};
+}
+
+auto Part1(Entry const& entry) -> bool {
+  auto const& [lo, hi, letter, text] = entry;
+  auto n = std::count(text.begin(), text.end(), letter);
+  return lo <= n && n <= hi;
+}
+
+auto Part2(Entry const& entry) -> bool
+{
+  auto const& [lo, hi, letter, text] = entry;
+  return (text.at(lo-1) == letter) != (text.at(hi-1) == letter);
+}
+
+} // namespace
+
+TEST_SUITE("documented examples") {
+
+TEST_CASE("parser") {
+  REQUIRE(Parse("1-3 z: example") == Entry{1,3,'z',"example"});
+}
+
+TEST_CASE("part 1") {
+  REQUIRE( Part1(Parse("1-3 a: abcde")));
+  REQUIRE(!Part1(Parse("1-3 b: cdefg")));
+  REQUIRE( Part1(Parse("2-9 c: ccccccccc")));
+}
+
+TEST_CASE("part 2") {
+  REQUIRE( Part2(Parse("1-3 a: abcde")));
+  REQUIRE(!Part2(Parse("1-3 b: cdefg")));
+  REQUIRE(!Part2(Parse("2-9 c: ccccccccc")));
+}
+
+}
+
+auto main(int argc, char** argv) -> int {
+  auto & in = aocpp::Startup(argc, argv);
+  std::uint64_t part1{}, part2{};
+  
+  std::string line;
+  while (std::getline(in, line)) {
+    auto entry = Parse(line);
+    if (Part1(entry)) part1++;
+    if (Part2(entry)) part2++;
+  }
+  std::cout << "Part 1: " << part1 << std::endl;
+  std::cout << "Part 2: " << part2 << std::endl;
+}
diff --git a/2020/03.cpp b/2020/03.cpp
new file mode 100644
index 0000000..d283873
--- /dev/null
+++ b/2020/03.cpp
@@ -0,0 +1,82 @@
+#include <algorithm>
+#include <cstdint>
+#include <iostream>
+#include <sstream>
+#include <tuple>
+#include <cstdio>
+#include <cstdlib>
+#include <numeric>
+#include <functional>
+
+#include <doctest.h>
+
+#include <aocpp/Startup.hpp>
+#include <aocpp/Grid.hpp>
+#include <aocpp/Coord.hpp>
+
+using aocpp::Startup;
+using aocpp::Coord;
+using aocpp::Grid;
+
+namespace {
+
+auto Ski(Grid const& grid, Coord step) -> std::size_t
+{
+  std::size_t const w = grid.rows[0].size();
+  std::size_t trees {0};
+  Coord here {0,0};
+
+  while(here.y < grid.rows.size()) {
+    if (grid[here] == '#') trees++;
+    here += step;
+    while (here.x >= w) { here.x -= w; }
+  }
+  return trees;
+}
+
+auto Part1(Grid const& grid) {
+  return Ski(grid, {3,1});
+}
+
+auto Part2(Grid const& grid) {
+  Coord const slopes[] = {{1,1}, {3,1}, {5,1}, {7,1}, {1,2}};
+  return std::transform_reduce(
+    std::begin(slopes), std::end(slopes),
+    1ULL, std::multiplies(),
+    [&](Coord slope) { return Ski(grid, slope); });
+}
+
+} // namespace
+
+TEST_SUITE("documented examples") {
+
+std::istringstream in {
+  "..##.......\n"
+  "#...#...#..\n"
+  ".#....#..#.\n"
+  "..#.#...#.#\n"
+  ".#...##..#.\n"
+  "..#.##.....\n"
+  ".#.#.#....#\n"
+  ".#........#\n"
+  "#.##...#...\n"
+  "#...##....#\n"
+  ".#..#...#.#\n"
+};
+auto grid = Grid::Parse(in);
+
+TEST_CASE("part 1") {
+  REQUIRE(Part1(grid) == 7);
+}
+
+TEST_CASE("part 2") {
+  REQUIRE(Part2(grid) == 336);
+}
+
+}
+
+auto main(int argc, char** argv) -> int {
+  auto grid = Grid::Parse(Startup(argc, argv));
+  std::cout << "Part 1: " << Part1(grid) << std::endl;
+  std::cout << "Part 2: " << Part2(grid) << std::endl;
+}
diff --git a/2020/CMakeLists.txt b/2020/CMakeLists.txt
index 93f0586..697d576 100644
--- a/2020/CMakeLists.txt
+++ b/2020/CMakeLists.txt
@@ -1,2 +1,5 @@
-add_executable(2020_01 01.cpp)
-target_link_libraries(2020_01 aocpp)
+add_executable(2020_02 02.cpp)
+target_link_libraries(2020_02 aocpp)
+
+add_executable(2020_03 03.cpp)
+target_link_libraries(2020_03 aocpp)
\ No newline at end of file