finish day 2

.gitignore

@@ -1,3 +1,5 @@
 cmake-*
 day1.dSYM
+build
 .idea
+.cache

CMakeLists.txt

@@ -3,11 +3,9 @@ project(cpp)
 
 set(CMAKE_CXX_STANDARD 23)
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexperimental-library")
+set(CMAKE_EXPORT_COMPILE_COMMANDS true)
 
-add_library(cpp STATIC
+add_executable(cpp_tests
         doctest.h
-        run_tests.cpp
+ 		run_tests.cpp
-        day1.cpp)
+)
-
-add_executable(cpp_tests run_tests.cpp)
-target_link_libraries(cpp_tests PRIVATE cpp)

day2.cpp

@@ -0,0 +1,190 @@
+#include <cassert>
+#include <charconv>
+#include <cmath>
+#include <cstdint>
+#include <ranges>
+#include <string>
+#include <fstream>
+#include <sstream>
+
+#include "doctest.h"
+
+namespace day2 {
+const std::string sample =
+        "11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,"
+        "446443-446449,38593856-38593862,565653-565659,824824821-824824827,"
+        "2121212118-2121212124";
+
+struct Range {
+    uint64_t start;
+    uint64_t end;
+};
+} // namespace day2
+
+template<>
+struct std::formatter<day2::Range> : std::formatter<std::string_view> {
+    static auto format(const day2::Range &i, std::format_context &ctx) {
+        return std::format_to(ctx.out(), "Range[start: {}, end: {}]", i.start, i.end);
+    }
+};
+
+namespace day2 {
+Range parse_range(std::string_view s) {
+    std::string_view start;
+    std::string_view end;
+
+    for (size_t i = 0; i < s.size(); i++) {
+        const char c = s[i];
+        if (c == '-') {
+            start = {s.data(), i};
+            end = {s.data() + i + 1, s.size() - start.size()};
+        }
+    }
+
+    Range range{};
+    uint64_t parsed;
+    std::from_chars(start.data(), start.end(), parsed);
+    range.start = parsed;
+    std::from_chars(end.data(), end.end(), parsed);
+    range.end = parsed;
+    return range;
+}
+
+size_t find_divisor(const uint64_t n) {
+    for (size_t i = 1;; i++) {
+        size_t div = n / std::pow(10, i);
+        if (div == 0) {
+            return std::pow(10, i / 2);
+        }
+    }
+    assert(0 && "Unreachable");
+}
+
+uint64_t count_repetitions(const Range range) {
+    uint64_t total = 0;
+    for (uint64_t n = range.start; n <= range.end; n++) {
+        auto div = find_divisor(n);
+        auto left = n / div;
+        auto right = n % div;
+        if (left == right) total++;
+    }
+
+    return total;
+}
+
+uint64_t sum_repetitions(const Range range) {
+    uint64_t total = 0;
+    for (uint64_t n = range.start; n <= range.end; n++) {
+        const auto div = find_divisor(n);
+        const auto left = n / div;
+        const auto right = n % div;
+        if (left == right) total += n;
+    }
+
+    return total;
+}
+
+uint64_t solve_first(std::string_view input) {
+    uint64_t result = 0;
+    for (const auto range:
+         std::views::split(input, ',') | std::views::transform([](auto s) {
+             return parse_range(std::string_view(s));
+         })) {
+        result += sum_repetitions(range);
+    }
+
+    return result;
+}
+
+uint64_t sum_repetitions_2(const Range range, std::string &buf) {
+    uint64_t total = 0;
+    for (uint64_t n = range.start; n <= range.end; n++) {
+        std::format_to(std::back_inserter(buf), "{}", n);
+        size_t size = buf.size();
+        for (int i = 0; i < size; ++i) {
+            if (size % i != 0 || size / i == 1) continue;
+            std::string_view first_partition(buf.data(), i);
+            bool all_equal = true;
+            for (int j = i; j < size; j += i) {
+                std::string_view partition(buf.data() + j, i);
+                if (partition != first_partition) {
+                    all_equal = false;
+                    break;
+                }
+            }
+
+            if (all_equal) {
+                total += n;
+                break;
+            }
+        }
+        buf.clear();
+    }
+
+    return total;
+}
+
+uint64_t solve_second(std::string_view input) {
+    std::string buf;
+    buf.reserve(100);
+    uint64_t result = 0;
+    for (const auto range:
+         std::views::split(input, ',') | std::views::transform([](auto s) {
+             return parse_range(std::string_view(s));
+         })) {
+        result += sum_repetitions_2(range, buf);
+        buf.clear();
+    }
+
+    return result;
+}
+
+
+TEST_CASE("Can parse input") {
+    auto range = parse_range("11-22");
+    CHECK(range.start == 11);
+    CHECK(range.end == 22);
+}
+
+TEST_CASE("Solve first sample") {
+    CHECK(solve_first(sample) == 1227775554);
+}
+
+TEST_CASE("Solve first input") {
+    std::ifstream fs("day2input.txt");
+    std::stringstream ss{};
+    ss << fs.rdbuf();
+    CHECK(solve_first(ss.str()) == 21898734247);
+}
+
+TEST_CASE("Find divisor works") {
+    CHECK(find_divisor(11) == 10);
+    CHECK(find_divisor(1221) == 100);
+    CHECK(find_divisor(222222) == 1000);
+}
+
+TEST_CASE("Count repetition works") {
+    CHECK(count_repetitions({.start = 11, .end = 22}) == 2);
+    CHECK(count_repetitions({.start = 1188511880, .end = 1188511890}) == 1);
+}
+
+TEST_CASE("sum_repetitions_2") {
+    std::string buf;
+    buf.reserve(100);
+    CHECK(sum_repetitions_2({95, 115}, buf) == 210);
+    buf.clear();
+    CHECK(sum_repetitions_2({998, 1012}, buf) == 999 + 1010);
+}
+
+TEST_CASE("Solves second sample") {
+    CHECK(solve_second(sample) == 4174379265);
+}
+
+TEST_CASE("Solves second input") {
+    std::ifstream fs("day2input.txt");
+    std::stringstream ss{};
+    ss << fs.rdbuf();
+    CHECK(solve_second(ss.view()) == 28915664389);
+}
+
+} // namespace day2

day2input.txt

@@ -0,0 +1 @@
+655-1102,2949-4331,885300-1098691,1867-2844,20-43,4382100-4484893,781681037-781860439,647601-734894,2-16,180-238,195135887-195258082,47-64,4392-6414,6470-10044,345-600,5353503564-5353567532,124142-198665,1151882036-1151931750,6666551471-6666743820,207368-302426,5457772-5654349,72969293-73018196,71-109,46428150-46507525,15955-26536,65620-107801,1255-1813,427058-455196,333968-391876,482446-514820,45504-61820,36235767-36468253,23249929-23312800,5210718-5346163,648632326-648673051,116-173,752508-837824

run_tests.cpp

@@ -5,3 +5,4 @@
 #define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
 #include "doctest.h"
 #include "day1.cpp"
+#include "day2.cpp"