From c2b969794f3e981d46852d7070cc64802be99e0d Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano@tronto.net>
Date: Fri, 6 Dec 2024 07:20:50 +0100
Subject: Day 6 2024

---
 2024/06/day06a.cpp | 152 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 152 insertions(+)
 create mode 100644 2024/06/day06a.cpp

(limited to '2024/06/day06a.cpp')

diff --git a/2024/06/day06a.cpp b/2024/06/day06a.cpp
new file mode 100644
index 0000000..69b9340
--- /dev/null
+++ b/2024/06/day06a.cpp
@@ -0,0 +1,152 @@
+#include <iostream>
+#include <algorithm>
+#include <string>
+#include <string_view>
+#include <vector>
+using namespace std;
+
+enum class Direction { U, D, R, L };
+Direction all_directions[] = {
+	Direction::U, Direction::D, Direction::R, Direction::L,
+};
+
+pair<int, int> step(pair<int, int> p, Direction d) {
+	auto [i, j] = p;
+
+	switch (d) {
+	case Direction::U:
+		return make_pair(i-1, j);
+	case Direction::D:
+		return make_pair(i+1, j);
+	case Direction::R:
+		return make_pair(i, j+1);
+	case Direction::L:
+		return make_pair(i, j-1);
+	}
+
+	return make_pair(-999,-999);
+}
+
+Direction turn(Direction d) {
+	switch (d) {
+	case Direction::U:
+		return Direction::R;
+	case Direction::D:
+		return Direction::L;
+	case Direction::R:
+		return Direction::D;
+	case Direction::L:
+		return Direction::U;
+	}
+
+	return Direction::U;
+}
+
+class Board {
+public:
+	const char out_of_bound = '$';
+	int M, N;
+
+	Board(vector<string> &lines) {
+		N = lines.size();
+		M = 0;
+		for (string l : lines)
+			M = max(M, (int)l.size());
+		cells = new char[M * N];
+		for (int i = 0; i < N; i++)
+			for (int j = 0; j < M; j++)
+				cells[N*i + j] = j < (int)lines[i].size() ?
+				    lines[i][j] : out_of_bound;
+	}
+
+	~Board() {
+		delete []cells;
+	}
+
+	char operator[](pair<int, int> p) {
+		int c = coord(p);
+		return c == -1 ? out_of_bound : cells[c];
+	}
+
+	bool is_obstruction(pair<int, int> p) {
+		return (*this)[p] == '#';
+	}
+
+	bool is_visited(pair<int, int> p) {
+		return (*this)[p] == 'x';
+	}
+
+	void set_visited(pair<int, int> p) {
+		int c = coord(p);
+		cells[c] = 'x';
+	}
+
+private:
+	char *cells;
+
+	int coord(pair<int, int> p) {
+		auto [i, j] = p;
+		return i >= N || i < 0 || j >= M || j < 0 ? -1 : N*i + j;
+	}
+};
+
+Direction guard_direction(char c) {
+	switch (c) {
+	case '^':
+		return Direction::U;
+	case 'v':
+		return Direction::D;
+	case '>':
+		return Direction::R;
+	case '<':
+		return Direction::L;
+	}
+
+	return Direction::U;
+}
+
+pair<pair<int, int>, Direction> find_guard(Board &board) {
+	pair<int, int> p(0, 0);
+	for (p.first = 0; p.first < board.N; p.first++) {
+		for (p.second = 0; p.second < board.M; p.second++) {
+			if (board[p] != '.' && board[p] != '#') {
+				Direction d = guard_direction(board[p]);
+				return make_pair(p, d);
+			}
+		}
+	}
+
+	return make_pair(make_pair(-999, -999), Direction::U);
+}
+
+int main() {
+	string line;
+	vector<string> lines;
+	while (getline(cin, line))
+		lines.push_back(line);
+
+	Board board(lines);
+
+	int tot = 1;
+	auto [p, d] = find_guard(board);
+	board.set_visited(p);
+
+	while (true) {
+		auto q = step(p, d);
+		if (board[q] == board.out_of_bound)
+			break;
+		if (board.is_obstruction(q)) {
+			d = turn(d);
+		} else {
+			p = q;
+			if (!board.is_visited(p)) {
+				board.set_visited(p);
+				tot++;
+			}
+		}
+	}
+
+	cout << tot << endl;
+
+	return 0;
+}
-- 
cgit v1.3