finish day 2

day2.cpp

@@ -41,7 +41,7 @@ namespace day2 {
         }
     }
 
-	Range range;
+    Range range{};
     uint64_t parsed;
     std::from_chars(start.data(), start.end(), parsed);
     range.start = parsed;
@@ -50,11 +50,11 @@ namespace day2 {
     return range;
 }
 
-  size_t find_divisor(uint64_t n) {
+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));
+            return std::pow(10, i / 2);
         }
     }
     assert(0 && "Unreachable");
@@ -75,9 +75,9 @@ namespace day2 {
 uint64_t sum_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;
+        const auto div = find_divisor(n);
+        const auto left = n / div;
+        const auto right = n % div;
         if (left == right) total += n;
     }
 
@@ -99,7 +99,26 @@ namespace day2 {
 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(buf, "{}", 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;
@@ -135,7 +154,7 @@ namespace day2 {
     std::ifstream fs("day2input.txt");
     std::stringstream ss{};
     ss << fs.rdbuf();
-	CHECK(solve_first(ss.str()) == 1227775554);
+    CHECK(solve_first(ss.str()) == 21898734247);
 }
 
 TEST_CASE("Find divisor works") {
@@ -149,4 +168,23 @@ namespace day2 {
     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