1 files changed, 187 insertions, 0 deletions

diff --git a/src/day03.cpp b/src/day03.cpp
new file mode 100644
index 0000000..d5e3fff
--- /dev/null
+++ b/src/day03.cpp
@@ -0,0 +1,187 @@
+#include <cctype>
+#include <fstream>
+#include <iostream>
+#include <string>
+#include <string_view>
+#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;
+}
+
+bool
+is_digit(char chr)
+{
+        return std::isdigit(static_cast<unsigned char>(chr)) != 0;
+}
+
+void
+part1() // NOLINT
+{
+        auto lines = read_file("data/day03.txt");
+
+        auto is_symbol = [&lines](int row, int col) -> bool {
+                static const string symbols{ "*#+$%=-@&/" };
+
+                if ( row < 0 || col < 0 ) {
+                        return false;
+                }
+                if ( size_t(row) >= lines.size() || size_t(col) >= lines[size_t(row)].size() ) {
+                        return false;
+                }
+
+                auto symbol = lines[size_t(row)][size_t(col)];
+
+                return symbols.find(symbol) != string::npos;
+        };
+
+        auto bordering = [&is_symbol](int row, int col) -> bool {
+                bool result = false;
+
+                result |= is_symbol(row - 1, col - 1);
+                result |= is_symbol(row - 0, col - 1);
+                result |= is_symbol(row + 1, col - 1);
+
+                result |= is_symbol(row - 1, col);
+                result |= is_symbol(row + 1, col);
+
+                result |= is_symbol(row - 1, col + 1);
+                result |= is_symbol(row - 0, col + 1);
+                result |= is_symbol(row + 1, col + 1);
+
+                return result;
+        };
+
+        auto sum = 0;
+        for ( size_t row = 0; row != lines.size(); ++row ) {
+                const auto& line = lines[row];
+
+                string::size_type start = 0;
+                while ( start != line.size() ) {
+                        while ( start != line.size() && !is_digit(line[start]) ) {
+                                ++start;
+                        }
+
+                        auto end = start;
+                        while ( end != line.size() && is_digit(line[end]) ) {
+                                ++end;
+                        }
+
+                        if ( start != end ) {
+                                auto result = false;
+
+                                for ( auto col = start; col != end; ++col ) {
+                                        result |= bordering(int(row), int(col));
+                                }
+
+                                if ( result ) {
+                                        sum += stoi(line.substr(start, end - start));
+                                }
+
+                                start = end;
+                        }
+                }
+        }
+        cout << sum << endl;
+}
+
+void
+part2()
+{
+        auto lines = read_file("data/day03.txt");
+
+        auto find_integer = [](vector<string>& lines, size_t row, size_t col, int& value) -> bool { // NOLINT
+                if ( row >= lines.size() || col >= lines[row].size() ) {
+                        return false;
+                }
+
+                auto& line = lines[row];
+
+                auto digit = line[col];
+
+                if ( !is_digit(digit) ) {
+                        return false;
+                }
+
+                // Anfang der Zahl suchen
+                auto start = col;
+                for ( ; start != 0 && is_digit(line[start - 1]); --start ) // NOLINT
+                        ;
+
+                auto end = col;
+                for ( ; end != line.size() && is_digit(line[end]); ++end ) // NOLINT
+                        ;
+
+                value = stoi(line.substr(start, end - start));
+
+                for ( ; start != end; ++start ) {
+                        line[start] = '.';
+                }
+
+                return true;
+        };
+
+        auto sum = 0;
+        for ( size_t row = 0; row != lines.size(); ++row ) {
+                const auto& line = lines[row];
+
+                auto col = line.find('*');
+                while ( col != string::npos ) {
+                        int value = 0;
+                        vector<int> values;
+                        auto lines_copy{ lines };
+
+                        if ( find_integer(lines_copy, row - 1, col - 1, value) ) {
+                                values.emplace_back(value);
+                        }
+                        if ( find_integer(lines_copy, row - 0, col - 1, value) ) {
+                                values.emplace_back(value);
+                        }
+                        if ( find_integer(lines_copy, row + 1, col - 1, value) ) {
+                                values.emplace_back(value);
+                        }
+
+                        if ( find_integer(lines_copy, row - 1, col, value) ) {
+                                values.emplace_back(value);
+                        }
+                        if ( find_integer(lines_copy, row + 1, col, value) ) {
+                                values.emplace_back(value);
+                        }
+
+                        if ( find_integer(lines_copy, row - 1, col + 1, value) ) {
+                                values.emplace_back(value);
+                        }
+                        if ( find_integer(lines_copy, row - 0, col + 1, value) ) {
+                                values.emplace_back(value);
+                        }
+                        if ( find_integer(lines_copy, row + 1, col + 1, value) ) {
+                                values.emplace_back(value);
+                        }
+
+                        if ( values.size() == 2 ) {
+                                auto ratio = values[0] * values[1];
+                                sum += ratio;
+                        }
+
+                        col = line.find('*', col + 1);
+                }
+        }
+        cout << sum << endl;
+}
+
+int
+main()
+{
+        part2();
+}