diff --git a/src/klotski_core/ffi/tmain.cc b/src/klotski_core/ffi/tmain.cc
index 7b1d7a2..f279941 100644
--- a/src/klotski_core/ffi/tmain.cc
+++ b/src/klotski_core/ffi/tmain.cc
@@ -56,11 +56,14 @@ void tmain() {
 //    Group::demo(RawCode::from_common_code(0x1A9BF0C00));
 //    Group::demo(RawCode::from_common_code(0x4FEA13400));
 
-//    std::cout << Group::demo(RawCode::from_common_code(0x1A9BF0C00)) << std::endl;
+//    auto ret = Group::group_cases(RawCode::from_common_code(0x1A9BF0C00));
+//    std::cout << ret.size() << std::endl;
+//    std::cout << ret[0] << std::endl;
+//    std::cout << ret[1] << std::endl;
 
     auto tmp = RawCode::from_common_code(0x1A9BF0C00);
     for (int i = 0; i < 100; ++i) {
-        Group::demo(tmp);
+        Group::group_cases(tmp);
     }
 
     std::cout << ((clock() - start) * 1000 / CLOCKS_PER_SEC) << "ms" << std::endl;
diff --git a/src/klotski_core/group/group.cc b/src/klotski_core/group/group.cc
index 4ef38b1..4ac2a61 100644
--- a/src/klotski_core/group/group.cc
+++ b/src/klotski_core/group/group.cc
@@ -1,4 +1,5 @@
 #include <queue>
+#include <vector>
 #include "core.h"
 #include "group.h"
 #include "common.h"
@@ -46,51 +47,37 @@ Group::block_num_t Group::block_num(const CommonCode &common_code) {
     return result;
 }
 
-uint32_t Group::demo(const RawCode &seed) {
+std::vector<RawCode> Group::group_cases(const RawCode &seed) {
     std::queue<uint64_t> cache;
-
-//    uint32_t index = 0;
-//    std::vector<uint64_t> temp;
-//    temp.reserve(65535 * 8);
-
-    absl::flat_hash_map<uint64_t, uint64_t> cases;
-
-    cases.reserve(65535 * 8);
-
+    absl::flat_hash_map<uint64_t, uint64_t> cases; // <code, mask>
+    cases.reserve(max_group_size(seed));
     cases.emplace(seed.unwrap(), 0); // without mask
     cache.emplace(seed.unwrap());
 
-//    temp.emplace_back(seed.unwrap());
-
     auto core = Core(
-        [&cases, &cache](auto &&code, auto &&mask) {
+        [&cache, &cases](auto &&code, auto &&mask) { // callback function
             auto current = cases.find(code);
-
             if (current != cases.end()) {
-                current->second |= mask; // update mask info
+                current->second |= mask; // update mask
                 return;
             }
-
             cases.emplace(code, mask);
             cache.emplace(code);
-//            temp.emplace_back(code);
-
         }
     );
-
-    while (!cache.empty()) {
-//    while (index != temp.size()) {
-
+    while (!cache.empty()) { // until BFS without elements
         core.next_cases(cache.front(), cases.find(cache.front())->second);
-//        core.next_cases(temp[index], cases.find(temp[index])->second);
-
-        cache.pop();
-//        ++index;
-
+        cache.pop(); // case dequeue
     }
 
-    return cases.size();
+    auto result = std::vector<RawCode>();
+    result.reserve(cases.size());
+    for (auto &&raw_code : cases) { // export group cases
+        result.emplace_back(RawCode::unsafe_create(raw_code.first));
+    }
+    return result;
 }
 
 
+
 } // namespace klotski
diff --git a/src/klotski_core/group/group.h b/src/klotski_core/group/group.h
index 9a3e184..956db25 100644
--- a/src/klotski_core/group/group.h
+++ b/src/klotski_core/group/group.h
@@ -15,10 +15,16 @@ public:
         uint8_t n_2x1 = 0;
     };
 
+//    static block_num_t block_num(uint32_t type_id);
     static block_num_t block_num(const RawCode &raw_code);
     static block_num_t block_num(const CommonCode &common_code);
 
-    static uint32_t demo(const RawCode &seed);
+//    static uint32_t max_group_size(uint32_t type_id);
+    static uint32_t max_group_size(const RawCode &raw_code) {
+        return 65535 * 8;
+    };
+
+    static std::vector<RawCode> group_cases(const RawCode &seed);
 
 };