aoc(2318): Lavaduct Lagoon

5 files changed, 197 insertions, 0 deletions

diff --git a/2023/18/Makefile b/2023/18/Makefile
new file mode 100644
index 0000000..af6a294
--- /dev/null
+++ b/2023/18/Makefile
@@ -0,0 +1,19 @@
+CXXFLAGS := -std=c++17
+CPPFLAGS := -I../include
+EXE := part1 part2
+
+.PHONY: all clean configure
+
+all: $(EXE)
+
+configure:
+        bear -- $(MAKE) all
+
+%.o: %.cpp
+        $(CXX) -c $(CPPFLAGS) $(CXXFLAGS) $< -o $@
+
+clean:
+        rm -rf $(EXE) src/*.o compile_commands.json
+
+%: src/%.o
+        $(CXX) $^ -o $@
diff --git a/2023/18/resources/input_small.txt b/2023/18/resources/input_small.txt
new file mode 100644
index 0000000..fc7612e
--- /dev/null
+++ b/2023/18/resources/input_small.txt
@@ -0,0 +1,14 @@
+R 6 (#70c710)
+D 5 (#0dc571)
+L 2 (#5713f0)
+D 2 (#d2c081)
+R 2 (#59c680)
+D 2 (#411b91)
+L 5 (#8ceee2)
+U 2 (#caa173)
+L 1 (#1b58a2)
+U 2 (#caa171)
+R 2 (#7807d2)
+U 3 (#a77fa3)
+L 2 (#015232)
+U 2 (#7a21e3)
diff --git a/2023/18/src/part1.cpp b/2023/18/src/part1.cpp
new file mode 100644
index 0000000..b7c9e09
--- /dev/null
+++ b/2023/18/src/part1.cpp
@@ -0,0 +1,62 @@
+#include <iostream>
+#include <fstream>
+#include <sstream>
+#include <deque>
+#include <vector>
+#include <tuple>
+
+#include "util.h"
+
+using Cmd = std::tuple<char,int>;
+using Pos = std::pair<int,int>;
+using Polygon = std::vector<Pos>;
+
+std::vector<Cmd> parse(const char* file)
+{
+    std::vector<Cmd> cmds;
+    if (std::ifstream input{ file }; input.is_open())
+    {
+        char dir; int steps;
+        std::string line;
+        while (not std::getline(input,line).eof())
+        {
+            std::stringstream in{ line };
+            in >> dir >> steps;
+            cmds.push_back({ dir, steps });
+        }
+    }
+    return cmds;
+}
+
+std::pair<int,Polygon> compute_border(Pos pos, const std::vector<Cmd>& cmds)
+{
+    Polygon poly;
+    int border{};
+    auto [x, y] = pos;
+    for(const auto& cmd : cmds)
+    {
+        auto [dir, steps] = cmd;
+        switch (dir)
+        {
+            case 'R': y += steps; break;
+            case 'D': x += steps; break;
+            case 'L': y -= steps; break;
+            case 'U': x -= steps;
+        }
+        poly.push_back({ x, y });
+        border += steps;
+    }
+    return { border, std::move(poly) };
+}
+
+
+
+int main(int argc, char* argv[])
+{
+    auto cmds = parse(argv[1]);
+    auto [border, polygon] = compute_border({ 0, 0 }, cmds);
+    int area = util::shoelace<int>(polygon.cbegin(), polygon.cend());
+
+    std::cout << border + util::pick(area, border) << std::endl;
+    return 0;
+}
diff --git a/2023/18/src/part2.cpp b/2023/18/src/part2.cpp
new file mode 100644
index 0000000..e9b6c02
--- /dev/null
+++ b/2023/18/src/part2.cpp
@@ -0,0 +1,63 @@
+#include <iostream>
+#include <fstream>
+#include <sstream>
+#include <vector>
+#include <tuple>
+
+#include "util.h"
+
+enum Dir { R = 0, D, L, U };
+using Cmd = std::tuple<Dir,long>;
+using Pos = std::pair<long,long>;
+using Polygon = std::vector<Pos>;
+
+std::vector<Cmd> parse(const char* file)
+{
+    std::vector<Cmd> cmds;
+    if (std::ifstream input{ file }; input.is_open())
+    {
+        Dir dir; int steps; std::string color;
+        std::string line;
+        while (not std::getline(input,line).eof())
+        {
+            std::stringstream in{ line };
+            in >> util::skip<char> >> util::skip<int> >> color;
+            steps = std::stoi(color.substr(2, 5), nullptr, 16);
+            dir = static_cast<Dir>(std::stoi(color.substr(7, 1)));
+            cmds.push_back({ dir, steps });
+        }
+    }
+    return cmds;
+}
+
+std::pair<long,Polygon> compute_border(Pos pos, const std::vector<Cmd>& cmds)
+{
+    Polygon poly;
+    long border{};
+    auto [x, y] = pos;
+    for(const auto& cmd : cmds)
+    {
+        auto [dir, steps] = cmd;
+        switch (dir)
+        {
+            case R: y += steps; break;
+            case D: x += steps; break;
+            case L: y -= steps; break;
+            case U: x -= steps;
+        }
+        poly.push_back({ x, y });
+        border += steps;
+    }
+    return { border, std::move(poly) };
+}
+
+int main(int argc, char* argv[])
+{
+    auto cmds = parse(argv[1]);
+    auto [border, polygon] = compute_border({ 0, 0 }, cmds);
+    long area = util::shoelace<long>(polygon.cbegin(), polygon.cend());
+
+    std::cout << border + util::pick(area, border) << std::endl;
+    return 0;
+}
+
diff --git a/2023/include/util.h b/2023/include/util.h
index e396e3c..3152719 100644
--- a/2023/include/util.h
+++ b/2023/include/util.h
@@ -6,6 +6,7 @@
 #include <stdexcept>
 #include <string>
 #include <string_view>
+#include <type_traits>
 
 namespace util
 {
@@ -119,6 +120,44 @@ std::basic_istream<CharT, Traits>& skip(std::basic_istream<CharT, Traits>& strea
     return stream;
 }
 
+/* @brief Compute the area of a planar simple polygon.
+ *
+ * @tparam Int integral coordinate type.
+ * @param first start of an iterator over pairs of 'Int'.
+ * @param last end of an iterator over pairs of 'Int'.
+ *
+ * @see https://en.wikipedia.org/wiki/Shoelace_formula#Triangle_formula
+ */
+template<typename Int, typename InputIt, typename = std::enable_if_t<std::is_integral_v<Int>,Int>>
+Int shoelace(InputIt first, InputIt last)
+{
+    Int result{};
+    auto [x1, y1] = *first;
+    while(first++ != last)
+    {
+        auto [x2, y2] = *first;
+        result += x1 * y2 - x2 * y1;
+        x1 = x2; y1 = y2;
+    }
+    return std::abs(result / 2);
+}
+
+/* @brief Return the number of integral coordinates inside a planar
+ *        simple polygon.
+ *
+ * @tparam Int integral return type.
+ * @param area the area of the polygon.
+ * @param border the number of integral coordinates on the polygon's
+ *        boundary.
+ * 
+ * @see https://en.wikipedia.org/wiki/Pick%27s_theorem#Formula
+ */
+template<typename Int = int, typename = std::enable_if_t<std::is_integral_v<Int>,Int>>
+Int pick(Int area, Int border)
+{
+    return area - border / 2 + 1;
+}
+
 } // namespace util
 
 #endif //UTIL_H