1 files changed, 144 insertions, 0 deletions

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();
+}