force solution

Change-Id: I1421c6279597b9cb040dfcafb6984a3730503d10

2025/day01.cpp

@@ -56,59 +56,64 @@ R14
 L82
 )";
 
-enum class rotdir {
-    none,
-    L,
-    R
-};
-
-struct rot {
-    rotdir dir;
-    u32 turns;
-};
-
-auto map_char_to_rotdir(char c) -> rotdir {
+auto map_char_to_rotdir(char c) -> i32 {
     switch (c) {
-        using enum rotdir;
-        case 'L': return L;
-        case 'R': return R;
-        default: return none;
+        case 'L': return -1;
+        case 'R':
+        default:  return 1;
     }
 }
 
-auto map_dir_to_i32(i32 value, rotdir dir) -> i32 {
-    switch (dir) {
-        using enum rotdir;
-        case L:  return -value;
-        case R:
-        default: return value;
-    } 
-}
-
 static auto entry([[maybe_unused]]std::span<char const*> const& args) -> void {
     // std::string str{raw_str};
-    // str = str | trim;
-    auto str = aoc::read_text("./input.txt").value_or("") | trim;
+    auto str = aoc::read_text("./input.txt").value_or("");
+    str = str | trim;
 
     auto rot_vec = str | std::views::split("\n"sv) | std::views::transform([](auto const& str) {
-            return rot{
-                .dir = map_char_to_rotdir(*std::begin(str)),
-                .turns = u32(std::stoul(std::string{++std::begin(str), std::end(str)}))
-            };
+            return i32(std::stoi(std::string{++std::begin(str), std::end(str)})) * map_char_to_rotdir(*std::begin(str));
         }) | std::ranges::to<std::vector>();
 
     i32 start = 50;
-    auto sum = std::ranges::fold_left(rot_vec, 0, [&start](auto a, auto b) {
-            auto c = map_dir_to_i32(b.turns % 100, b.dir);
+    i32 zero_cross = 0;
+    // auto sum = std::ranges::fold_left(rot_vec, 0, [&](auto a, auto t) {
+    //         auto const p = start;
+    //         start = (100 + p - t) % 100;
+    //
+    //         zero_cross += (std::abs((p - t + 1) % 100) + std::abs(t)) / 100;
+    //
+    //         fmt::print("pos: {}, next: {}, t: {}\n", p, start, t);
+    //
+    //         if (start == 0) {
+    //             a += 1;
+    //         }
+    //
+    //         return a;
+    //     });
 
-            start = (100 + start + c) % 100;
+    auto sum = std::ranges::fold_left(rot_vec, 0, [&](auto a, auto t) {
+            auto const dir = t < 0 ? -1 : 1;
+            auto const steps = std::abs(t);
 
-            if (start == 0) ++a;
+            for (i32 i = 0; i < steps; ++i) {
+                auto next = start + dir;
+                if (next < 0) next = 99;
+                next = next % 100;
 
+                if (next % 100 == 0)
+                    ++zero_cross;
+
+                start = next;
+            }
+
+            if (start % 100 == 0) {
+                ++a;
+                if (zero_cross > 0)
+                    zero_cross -= 1;
+            }
             return a;
         });
 
-    fmt::print("res: {}\n", sum);
+    fmt::print("res: {}, {} sum = {}\n", sum, zero_cross, sum + zero_cross);
 }
 
 auto main([[maybe_unused]]int argc, [[maybe_unused]]char const* argv[]) -> int {