Day 11.

blaz-kranjc · Dec 11, 2020 · 3481a48 · 3481a48
1 parent 9c0433c
commit 3481a48
Showing 5 changed files with 253 additions and 2 deletions.
diff --git a/resources/day11.txt b/resources/day11.txt
@@ -0,0 +1,93 @@
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diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
@@ -23,3 +23,4 @@ aoc2020(7)
 aoc2020(8)
 aoc2020(9)
 aoc2020(10)
+aoc2020(11)
diff --git a/src/day10.cpp b/src/day10.cpp
@@ -2,7 +2,6 @@
 
 #include <range/v3/all.hpp>
 #include <fmt/core.h>
-#include <iostream>
 #include <unordered_set>
 #include <unordered_map>
 #include <algorithm>

diff --git a/src/day11.cpp b/src/day11.cpp
@@ -0,0 +1,159 @@
+#include "input_file_loader.h"
+
+#include <range/v3/all.hpp>
+#include <fmt/core.h>
+#include <utility>
+
+template <typename T>
+class PaddedVector2D
+{
+public:
+  PaddedVector2D(std::size_t n_cols, T m_padding_value, std::vector<T> raw)
+    : m_raw{ std::move(raw) }
+    , m_n_cols{ n_cols }
+    , m_padding_value{ std::move(m_padding_value) }
+  {}
+
+  const T& at(int row, int column) const
+  {
+    if (row < 0 || row > rows() - 1 || column < 0 || column > cols() - 1) {
+      return m_padding_value;
+    } else {
+      return m_raw[index(row, column)];
+    }
+  }
+
+  T& at(int row, int column)
+  {
+    if (row < 0 || row > rows() - 1 || column < 0 || column > cols() - 1) {
+      return m_padding_value;
+    } else {
+      return m_raw[index(row, column)];
+    }
+  }
+
+  std::size_t rows() const
+  {
+    return m_raw.size() / m_n_cols;
+  }
+
+  std::size_t cols() const
+  {
+    return m_n_cols;
+  }
+
+  const std::vector<T>& raw() const
+  {
+    return m_raw;
+  }
+
+private:
+  std::size_t index(int row, int column) const
+  {
+    return m_n_cols * row + column;
+  };
+
+  std::vector<T> m_raw;
+  std::size_t m_n_cols;
+  T m_padding_value;
+};
+
+enum class SeatState {
+  Empty,
+  Occupied,
+  Missing
+};
+
+PaddedVector2D<SeatState> parse(std::istream &&is) {
+  std::vector<SeatState> result;
+  std::size_t column_size = 0;
+  for (std::string line; std::getline(is, line);) {
+    if (column_size == 0) column_size = line.size();
+    ranges::transform(
+      line,
+      std::back_inserter(result),
+      [](char c) { return c == 'L' ? SeatState::Empty : SeatState::Missing; });
+  }
+
+  return PaddedVector2D{ column_size, SeatState::Empty, std::move(result) };
+}
+
+constexpr std::array neighbours {
+  std::pair{-1, -1},
+  std::pair{-1, 0},
+  std::pair{-1, 1},
+  std::pair{0, -1},
+  std::pair{0, 1},
+  std::pair{1, -1},
+  std::pair{1, 0},
+  std::pair{1, 1},
+};
+
+constexpr auto count_neighbours_1 = [](const PaddedVector2D<SeatState>& data, int row, int column)
+{
+  return ranges::count(
+    neighbours
+      | ranges::views::transform([&data, row, column](auto p) { return data.at(p.first + row, p.second + column); }),
+    SeatState::Occupied);
+};
+
+constexpr auto next_state_1 = [](SeatState old, int neighbours) {
+  if (old == SeatState::Occupied && neighbours >= 4)
+    return SeatState::Empty;
+  else if (old == SeatState::Empty && neighbours == 0)
+    return SeatState::Occupied;
+  else
+    return old;
+};
+
+constexpr auto count_neighbours_2 = [](const PaddedVector2D<SeatState>& data, int row, int column)
+{
+  return ranges::count(
+    neighbours
+      | ranges::views::transform([&data, row, column](auto p) { 
+          auto r = p.first + row;
+          auto c = p.second + column;
+          while (data.at(r, c) == SeatState::Missing) {
+            r += p.first;
+            c += p.second;
+          }
+          return data.at(r, c);
+      }),
+    SeatState::Occupied);
+};
+
+constexpr auto next_state_2 = [](SeatState old, int neighbours) {
+  if (old == SeatState::Occupied && neighbours >= 5)
+    return SeatState::Empty;
+  else if (old == SeatState::Empty && neighbours == 0)
+    return SeatState::Occupied;
+  else
+    return old;
+};
+
+template <auto next_state, auto count_neighbours>
+PaddedVector2D<SeatState> simulate_until_steady(PaddedVector2D<SeatState> arrangement)
+{
+  int diff = 0;
+  auto old = arrangement;
+  do {
+    diff = 0;
+    for (int row = 0; row < arrangement.rows(); ++row) {
+      for (int column = 0; column < arrangement.cols(); ++column) {
+        const auto old_value = old.at(row, column);
+        const auto new_value = next_state(old_value, count_neighbours(old, row, column));
+        if (old_value != new_value) { ++diff; }
+        arrangement.at(row, column) = new_value;
+      }
+    }
+    std::swap(arrangement, old);
+  } while (diff > 0);
+  return old;
+}
+
+int main(int argc, char **argv)
+{
+  auto data = parse(load_input(argc, argv));
+  fmt::print("Part 1: {}\n", ranges::count(simulate_until_steady<next_state_1, count_neighbours_1>(data).raw(), SeatState::Occupied));
+  fmt::print("Part 2: {}\n", ranges::count(simulate_until_steady<next_state_2, count_neighbours_2>(data).raw(), SeatState::Occupied));
+}
diff --git a/src/day9.cpp b/src/day9.cpp
@@ -3,7 +3,6 @@
 #include <range/v3/all.hpp>
 #include <fmt/core.h>
 #include <vector>
-#include <iostream>
 
 std::vector<long long> parse(std::istream&& is)
 {