From 1165d51cc10b5795e1ec78f3eb5c9b56bfb31d18 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 10 Dec 2023 10:41:42 +0100
Subject: Lösung für Tag 10, Teil 1
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---
 makefile      |   3 +-
 src/day10.cpp | 144 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 146 insertions(+), 1 deletion(-)
 create mode 100644 src/day10.cpp

diff --git a/makefile b/makefile
index 2e63b97..0b89873 100644
--- a/makefile
+++ b/makefile
@@ -8,7 +8,8 @@ all: bin/day01 \
 	 bin/day06 \
 	 bin/day07 \
 	 bin/day08 \
-	 bin/day09
+	 bin/day09 \
+	 bin/day10
 
 bin:
 	mkdir $@
diff --git a/src/day10.cpp b/src/day10.cpp
new file mode 100644
index 0000000..b9d6355
--- /dev/null
+++ b/src/day10.cpp
@@ -0,0 +1,144 @@
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <vector>
+using namespace std;
+
+vector<string>
+read_file(string_view filename)
+{
+	fstream        input{ filename };
+	vector<string> data;
+
+	for ( string line; getline(input, line); ) {
+		data.emplace_back(line);
+	}
+
+	return data;
+}
+
+void
+part1()
+{
+	typedef tuple<size_t, size_t> pos_t;
+
+	const auto puzzle = read_file("data/day10.txt");
+
+	const auto find_start_pos = [&]() -> pos_t {
+		for ( size_t y = 0; y != puzzle.size(); ++y ) { // NOLINT
+			auto x = puzzle[y].find('S');               // NOLINT
+			if ( x != string::npos ) {
+				return { x, y };
+			}
+		}
+
+		return { 0, 0 };
+	};
+
+	const auto predict_direction = [&](pos_t& current, char& direction) -> bool {
+		auto x = get<0>(current); // NOLINT
+		auto y = get<1>(current); // NOLINT
+
+		if ( direction == 'S' ) {
+			++y;
+			if ( y >= puzzle.size() ) {
+				return false;
+			}
+			auto tile = puzzle[y][x];
+			if ( tile != 'J' && tile != '|' && tile != 'L' ) {
+				return false;
+			}
+			if ( tile == 'J' ) {
+				direction = 'W';
+			}
+			else if ( tile == 'L' ) {
+				direction = 'E';
+			}
+		}
+		else if ( direction == 'N' ) {
+			--y;
+			if ( y >= puzzle.size() ) {
+				return false;
+			}
+			auto tile = puzzle[y][x];
+			if ( tile != '7' && tile != '|' && tile != 'F' ) {
+				return false;
+			}
+			if ( tile == '7' ) {
+				direction = 'W';
+			}
+			else if ( tile == 'F' ) {
+				direction = 'E';
+			}
+		}
+		else if ( direction == 'E' ) {
+			++x;
+			if ( x >= puzzle[y].size() ) {
+				return false;
+			}
+			auto tile = puzzle[y][x];
+			if ( tile != 'J' && tile != '-' && tile != '7' ) {
+				return false;
+			}
+			if ( tile == 'J' ) {
+				direction = 'N';
+			}
+			else if ( tile == '7' ) {
+				direction = 'S';
+			}
+		}
+		else if ( direction == 'W' ) {
+			--x;
+			if ( x >= puzzle[y].size() ) {
+				return false;
+			}
+			auto tile = puzzle[y][x];
+			if ( tile != 'L' && tile != '-' && tile != 'F' ) {
+				return false;
+			}
+			if ( tile == 'L' ) {
+				direction = 'N';
+			}
+			else if ( tile == 'F' ) {
+				direction = 'S';
+			}
+		}
+		else {
+			cerr << "invalid direction " << direction << ")!" << endl;
+			return false;
+		}
+
+		current = { x, y };
+		return true;
+	};
+
+	const auto start_pos = find_start_pos();
+
+	auto max_steps = 0;
+
+	for ( const auto direction: { 'N', 'S', 'E', 'W' } ) {
+		auto current_direction = direction;
+		auto current_pos       = start_pos;
+
+		auto steps = 0;
+		for ( ;; ) {
+			++steps;
+
+			if ( !predict_direction(current_pos, current_direction) ) {
+				break;
+			}
+		}
+		cout << "Richtung: " << direction << " - Schritte: " << steps << endl;
+
+		max_steps = max(max_steps, steps);
+	}
+
+	cout << max_steps / 2 << endl;
+}
+
+int
+main()
+{
+	part1();
+}
-- 
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