From e2a90aab7febe9ca73661d17a26fcb0dd10a68a7 Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano@tronto.net>
Date: Sun, 15 Dec 2024 09:05:08 +0100
Subject: Day 15 2024

---
 2024/15/day15a.cpp | 141 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 141 insertions(+)
 create mode 100644 2024/15/day15a.cpp

(limited to '2024/15/day15a.cpp')

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;
+}
-- 
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