1 files changed, 141 insertions, 0 deletions

diff --git a/2024/15/day15a.cpp b/2024/15/day15a.cpp
new file mode 100644
index 0000000..90b271a
--- /dev/null
+++ b/2024/15/day15a.cpp
@@ -0,0 +1,141 @@
+#include <iostream>
+#include <cstdint>
+#include <algorithm>
+#include <string>
+#include <string_view>
+#include <vector>
+#include <set>
+using namespace std;
+
+class Direction {
+public:
+        const int U, R;
+
+        Direction(char c) :
+            U{c == 'v' ? 1 : (c == '^' ? -1 : 0)},
+            R{c == '>' ? 1 : (c == '<' ? -1 : 0)} {}
+
+        Direction(const int i, const int j) : U{i}, R{j} {}
+
+        Direction turnright() const {
+                return turn(-1, 0);
+        }
+
+        Direction turnleft() const {
+                return turn(1, 0);
+        }
+
+        bool operator<(const Direction& d) const { // For set<Direction>
+                return this->U < d.U || (this->U == d.U && this->R < d.R);
+        }
+private:
+        Direction turn(int64_t sin, int64_t cos) const {
+                return Direction(cos * U - sin * R, sin * U + cos * R);
+        }
+};
+
+class Position {
+public:
+        int64_t i, j;
+
+        Position() : Position(0, 0) {}
+
+        Position(int64_t a, int64_t b) : i{a}, j{b} {}
+
+        Position step(const Direction d) const {
+                return Position(i+d.U, j+d.R);
+        }
+};
+
+const Direction all_directions[] = {
+        Direction(1, 0), Direction(-1, 0), Direction(0, 1), Direction(0, -1)
+};
+
+class Board {
+public:
+        int64_t N, M;
+        Position robot;
+
+        Board(const vector<string>& lines) :
+            N{static_cast<int64_t>(lines.size())},
+            M{static_cast<int64_t>(lines[0].size())},
+            cells(M*N)
+        {
+                for (int64_t i = 0; i < N; i++) {
+                        for (int64_t j = 0; j < M; j++) {
+                                cells[N*i+j] = lines[i][j];
+                                if (lines[i][j] == '@')
+                                        robot = Position(i, j);
+                        }
+                }
+        }
+
+        char& operator[](const Position p) {
+                if (const auto c = coord(p); c == -1)
+                        return out_of_bound;
+                else
+                        return cells[c];
+        }
+
+        void move_robot(const Direction d) {
+                if (move(robot, d))
+                        robot = robot.step(d);
+        }
+
+        int64_t gps() {
+                int64_t tot = 0;
+                for (Position p(0, 0); p.i < N; p.i++)
+                        for (p.j = 0; p.j < M; p.j++)
+                                if ((*this)[p] == 'O')
+                                        tot += 100*p.i + p.j;
+                return tot;
+        }
+
+        void print() {
+                for (Position p(0, 0); p.i < N; p.i++) {
+                        for (p.j = 0; p.j < M; p.j++)
+                                cout << (*this)[p];
+                        cout << endl;
+                }
+        }
+private:
+        char out_of_bound = '$';
+
+        vector<char> cells;
+
+        int64_t coord(const Position p) const {
+                auto [i, j] = p;
+                return i >= N || i < 0 || j >= M || j < 0 ? -1 : N * i + j;
+        }
+
+        bool move(Position p, Direction d) {
+                auto q = p.step(d);
+                switch ((*this)[q]) {
+                case '.':
+                        (*this)[q] = (*this)[p];
+                        (*this)[p] = '.';
+                        return true;
+                case 'O':
+                        return move(q, d) ? move(p, d) : false;
+                default:
+                        return false;
+                }
+        }
+};
+
+int main() {
+        string line;
+        vector<string> lines;
+
+        for (getline(cin, line); line.size() > 0; getline(cin, line))
+                lines.push_back(line);
+        Board board(lines);
+
+        while (getline(cin, line))
+                for (const auto& c : line)
+                        board.move_robot(Direction(c));
+
+        cout << board.gps() << endl;
+
+        return 0;
+}