From e37fec36f858db4fb098afb98e18c6fd1bae5640 Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@galois.com>
Date: Wed, 18 Jan 2023 15:24:18 -0800
Subject: [PATCH] 2022-12

---
 2022/12.cpp         | 92 +++++++++++++++++++++++++++++++++++++++++++++
 2022/CMakeLists.txt |  3 ++
 2 files changed, 95 insertions(+)
 create mode 100644 2022/12.cpp

diff --git a/2022/12.cpp b/2022/12.cpp
new file mode 100644
index 0000000..f0d9993
--- /dev/null
+++ b/2022/12.cpp
@@ -0,0 +1,92 @@
+#include <cstdint>
+#include <iostream>
+#include <set>
+#include <sstream>
+#include <tuple>
+#include <vector>
+
+#include <doctest.h>
+
+#include <aocpp/Coord.hpp>
+#include <aocpp/Grid.hpp>
+#include <aocpp/Startup.hpp>
+
+using aocpp::Coord;
+using aocpp::Grid;
+
+namespace {
+
+auto Parse(std::istream & in) -> std::tuple<Coord, Coord, Grid>
+{
+  Coord start {};
+  Coord end {};
+  auto grid = Grid::Parse(in);
+
+  grid.each([&](Coord c, char v) {
+    switch (v) {
+      case 'S': grid[c] = 'a'; start = c; break;
+      case 'E': grid[c] = 'z'; end   = c; break;
+    }
+  });
+
+  return {start, end, std::move(grid)};
+}
+
+auto Solve(std::vector<Coord> starts, Coord end, Grid const& grid) -> std::int64_t
+{
+  std::vector<Coord> prev_layer(std::move(starts));
+  std::vector<Coord> next_layer;
+  std::set<Coord> seen;
+  std::int64_t counter {1};
+
+  while (!prev_layer.empty()) {
+    for (auto here : prev_layer) {
+      if (!seen.insert(here).second) continue;
+      auto here_height = grid[here];
+      for (auto next : {Up(here), Down(here), Left(here), Right(here)}) {
+        if (!grid.contains(next)) continue;
+        if (grid[next] - here_height > 1) continue;
+        if (next == end) { return counter; }
+        next_layer.push_back(next);
+      }
+    }
+    counter++;
+    prev_layer.clear();
+    std::swap(prev_layer, next_layer);
+  }
+
+  return -1;
+}
+
+auto Part2Starts(Grid const& grid) -> std::vector<Coord>
+{
+    std::vector<Coord> starts;
+    grid.each([&](Coord c, char v) {
+      if (v == 'a') starts.push_back(c);
+    });
+    return starts;
+}
+
+} // namespace
+
+TEST_SUITE("2022-12 examples") {
+  TEST_CASE("documented example") {
+    std::istringstream in {
+      "Sabqponm\n"
+      "abcryxxl\n"
+      "accszExk\n"
+      "acctuvwj\n"
+      "abdefghi\n"
+    };
+    auto [start, end, grid] = Parse(in);
+    CHECK(31 == Solve({start}, end, grid));
+    CHECK(29 == Solve(Part2Starts(grid), end, grid));
+  }
+}
+
+auto main(int argc, char** argv) -> int
+{
+  auto [start, end, grid] = Parse(*aocpp::Startup(argc, argv));
+  std::cout << "Part 1: " << Solve({start}, end, grid) << std::endl;
+  std::cout << "Part 2: " << Solve(Part2Starts(grid), end, grid) << std::endl;
+}
diff --git a/2022/CMakeLists.txt b/2022/CMakeLists.txt
index a9fe453..76613ed 100644
--- a/2022/CMakeLists.txt
+++ b/2022/CMakeLists.txt
@@ -7,5 +7,8 @@ target_link_libraries(2022_03 aocpp)
 add_executable(2022_04 04.cpp)
 target_link_libraries(2022_04 aocpp)
 
+add_executable(2022_12 12.cpp)
+target_link_libraries(2022_12 aocpp)
+
 add_executable(2022_25 25.cpp)
 target_link_libraries(2022_25 aocpp)