2024 day 25: solve part 1

2024/answer_tests/day25/example1.txt

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+Day 25:
+3

2024/input/day25/example1.txt

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+#####
+.####
+.####
+.####
+.#.#.
+.#...
+.....
+
+#####
+##.##
+.#.##
+...##
+...#.
+...#.
+.....
+
+.....
+#....
+#....
+#...#
+#.#.#
+#.###
+#####
+
+.....
+.....
+#.#..
+###..
+###.#
+###.#
+#####
+
+.....
+.....
+.....
+#....
+#.#..
+#.#.#
+#####

2024/src/day25.cpp

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+/******************************************************************************
+ * File:        day25.cpp
+ *
+ * Author:      Eric T. Johnson (yut23)
+ * Created:     2025-01-27
+ *****************************************************************************/
+
+#include "day25.hpp"
+#include "lib.hpp"
+#include <fstream>  // for ifstream
+#include <iostream> // for cout
+
+int main(int argc, char **argv) {
+    std::ifstream infile = aoc::parse_args(argc, argv).infile;
+
+    auto [keys, locks] = aoc::day25::read_input(infile);
+
+    int count = 0;
+    for (const auto &lock : locks) {
+        if constexpr (aoc::DEBUG) {
+            std::cerr << "checking " << lock << ":\n";
+        }
+        for (const auto &key : keys) {
+            if constexpr (aoc::DEBUG) {
+                std::cerr << "  " << key << "";
+            }
+            if (lock.check_fit(key)) {
+                if constexpr (aoc::DEBUG) {
+                    std::cerr << ": fits";
+                }
+                ++count;
+            }
+            if constexpr (aoc::DEBUG) {
+                std::cerr << "\n";
+            }
+        }
+    }
+    std::cout << count << "\n";
+
+    return 0;
+}

2024/src/day25.hpp

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+/******************************************************************************
+ * File:        day25.hpp
+ *
+ * Author:      Eric T. Johnson (yut23)
+ * Created:     2025-01-27
+ *****************************************************************************/
+
+#ifndef DAY25_HPP_DOJZBHTX
+#define DAY25_HPP_DOJZBHTX
+
+#include "unit_test/pretty_print.hpp" // for repr
+
+#include <array>    // for array
+#include <iostream> // for istream
+#include <string>   // for string, getline
+#include <utility>  // for pair
+#include <vector>   // for vector
+
+namespace aoc::day25 {
+
+struct Schematic {
+    bool is_key;
+    std::array<char, 5> pins;
+
+    bool check_fit(const Schematic &other) const {
+        if (this->is_key == other.is_key) {
+            return false;
+        }
+        if (this->is_key) {
+            return other.check_fit(*this);
+        }
+        // *this is a lock, other is a key
+        for (unsigned int i = 0; i < pins.size(); ++i) {
+            if (pins[i] + other.pins[i] > 5) {
+                return false;
+            }
+        }
+        return true;
+    }
+};
+
+std::istream &operator>>(std::istream &is, Schematic &schematic) {
+    Schematic tmp{};
+    std::string line;
+    // consume blank line if present
+    is >> std::ws;
+    if (!std::getline(is, line)) {
+        return is;
+    }
+    tmp.is_key = line[0] == '.';
+    for (int i = 0; i < 5; ++i) {
+        if (!std::getline(is, line)) {
+            break;
+        }
+        for (int j = 0; j < 5; ++j) {
+            tmp.pins[j] += line[j] == '#';
+        }
+    }
+    std::getline(is, line);
+    if (is) {
+        std::swap(schematic, tmp);
+    }
+    return is;
+}
+
+std::ostream &operator<<(std::ostream &os, const Schematic &schematic) {
+    os << (schematic.is_key ? "key" : "lock") << " ";
+    os << pretty_print::repr(schematic.pins, {.char_as_number = true});
+    return os;
+}
+
+std::pair<std::vector<Schematic>, std::vector<Schematic>>
+read_input(std::istream &is) {
+    std::vector<Schematic> keys;
+    std::vector<Schematic> locks;
+    Schematic schematic;
+    while (is >> schematic) {
+        if (schematic.is_key) {
+            keys.push_back(std::move(schematic));
+        } else {
+            locks.push_back(std::move(schematic));
+        }
+    }
+    return {keys, locks};
+}
+
+} // namespace aoc::day25
+
+#endif /* end of include guard: DAY25_HPP_DOJZBHTX */