finish day 1

day1.cpp

@@ -0,0 +1,129 @@
+//
+// Created by Grant Horner on 12/1/25.
+//
+
+#include <cassert>
+#include <charconv>
+#include <ranges>
+#include <fstream>
+#include <sstream>
+
+#include "doctest.h"
+
+enum Direction {
+    L = 'L',
+    R = 'R',
+};
+
+struct Instruction {
+    Direction direction;
+    uint32_t amount;
+};
+
+Instruction parse_instruction(std::string_view line) {
+    assert(!line.empty());
+    const auto direction = static_cast<Direction>(line[0]);
+    uint32_t amount;
+    std::from_chars(&line[1], line.data() + line.size(), amount);
+    return Instruction{direction, amount};
+}
+
+template<>
+struct std::formatter<Instruction> : std::formatter<string_view> {
+    static auto format(const Instruction &i, std::format_context &ctx) {
+        return std::format_to(ctx.out(), "Instruction[direction: {}, amount: {}]", static_cast<char>(i.direction),
+                              i.amount);
+    }
+};
+
+const std::string sample =
+        "L68\n"
+        "L30\n"
+        "R48\n"
+        "L5\n"
+        "R60\n"
+        "L55\n"
+        "L1\n"
+        "L99\n"
+        "R14\n"
+        "L82\n";
+
+uint64_t spin2(int &value, Instruction i) {
+    uint64_t spins = i.amount / 100;
+    int amount_to_spin = i.amount % 100;
+    if (i.direction == L) {
+        amount_to_spin *= -1;
+    }
+
+    value += amount_to_spin;
+    if (value == 0) {
+        spins++;
+    } else if (value < 0) {
+        spins++;
+        value = 100 + value;
+    } else if (100 < value) {
+        spins++;
+        value = value - 100;
+    }
+    return spins;
+}
+
+bool spin(int &value, Instruction i) {
+    value += static_cast<int>(i.amount) * (i.direction == L ? -1 : 1);
+    value %= 100;
+    return value == 0;
+}
+
+uint32_t solve_first(const std::string &input) {
+    int value = 50;
+    uint32_t spins = 0;
+
+    for (const auto instr:
+         std::views::split(input, '\n')
+         | std::views::transform([](auto s) { return std::string_view(s); })
+         | std::views::filter([](const std::string_view s) { return !s.empty(); })
+         | std::views::transform(parse_instruction)
+    ) {
+        if (spin(value, instr)) {
+            spins++;
+        }
+        // std::println("Total spins: {}, instruction: {}, value: {}", spins, instr, value);
+    }
+
+    return spins;
+}
+
+TEST_CASE("puzzle 1") {
+    CHECK(solve_first(sample) == 3);
+    std::ifstream input("day1input.txt");
+    CHECK(input.is_open());
+    std::stringstream buffer;
+    buffer << input.rdbuf();
+    CHECK(solve_first(buffer.str()) == 1158);
+}
+
+uint32_t solve_second(const std::string &input) {
+    int value = 50;
+    uint32_t spins = 0;
+
+    for (const auto instr:
+         std::views::split(input, '\n')
+         | std::views::transform([](auto s) { return std::string_view(s); })
+         | std::views::filter([](const std::string_view s) { return !s.empty(); })
+         | std::views::transform(parse_instruction)
+    ) {
+        spins += spin2(value, instr);
+        // std::println("Total spins: {}, instruction: {}, value: {}", spins, instr, value);
+    }
+
+    return spins;
+}
+
+TEST_CASE("puzzle 2") {
+    CHECK(solve_second(sample) == 6);
+    std::ifstream input("day1input.txt");
+    CHECK(input.is_open());
+    std::stringstream buffer;
+    buffer << input.rdbuf();
+    CHECK(solve_second(buffer.str()) == 6860);
+}