diff --git a/src/core/fast_cal/internal/layer_queue.inl b/src/core/fast_cal/internal/layer_queue.inl
index 588fd2a..d71ec1e 100644
--- a/src/core/fast_cal/internal/layer_queue.inl
+++ b/src/core/fast_cal/internal/layer_queue.inl
@@ -3,98 +3,71 @@
 namespace klotski {
 
 template <typename T>
-LayerQueue<T>::LayerQueue(std::initializer_list<T> first_layer, const size_t reserve) {
-    // data_.resize(reserve);
-
-    static_assert(std::is_trivial_v<T>);
-
-    // data_ = new T[reserve];
-    data_ = (T*)std::malloc(sizeof(T) * reserve);
-
-    queue_begin_ = 0;
-    queue_end_ = 0;
-    for (auto x : first_layer) {
-        emplace(x);
+requires std::is_trivial_v<T>
+LayerQueue<T>::LayerQueue(std::initializer_list<T> first_layer, const size_t max_size)
+        : layer_end_(first_layer.size()), queue_end_(0) {
+    data_ = static_cast<T*>(std::malloc(sizeof(T) * max_size));
+    for (const auto node : first_layer) {
+        emplace(node);
     }
-
-    layer_begin_ = 0;
-    layer_end_ = first_layer.size();
-
-    layers_.reserve(139);
-//    layers_.emplace_back(0, layer_end_);
-    layers_.emplace_back(0);
-    layers_.emplace_back(layer_end_);
+    layer_offset_.reserve(139); // TODO: confirm the max layer number
+    layer_offset_.emplace_back(layer_end_);
 }
 
 template <typename T>
+requires std::is_trivial_v<T>
 LayerQueue<T>::~LayerQueue() {
-    // delete []data_;
     std::free(data_);
 }
 
 template <typename T>
-void LayerQueue<T>::emplace(T node) {
-    data_[queue_end_] = node;
-    ++queue_end_;
+requires std::is_trivial_v<T>
+T LayerQueue<T>::current() const {
+    return data_[queue_begin_];
 }
 
 template <typename T>
-T LayerQueue<T>::current() const {
-    return data_[queue_begin_];
+requires std::is_trivial_v<T>
+void LayerQueue<T>::emplace(T node) {
+    data_[queue_end_] = node;
+    ++queue_end_;
 }
 
 template <typename T>
+requires std::is_trivial_v<T>
 void LayerQueue<T>::next() {
     ++queue_begin_;
     if (queue_begin_ == layer_end_ && !is_ending()) {
         layer_begin_ = layer_end_;
         layer_end_ = queue_end_;
-//        layers_.emplace_back(layer_begin_, layer_end_);
-        layers_.emplace_back(layer_end_);
+        layer_offset_.emplace_back(layer_end_);
     }
 }
 
 template <typename T>
+requires std::is_trivial_v<T>
 [[nodiscard]] bool LayerQueue<T>::is_ending() const {
     return queue_begin_ == queue_end_;
 }
 
 template <typename T>
+requires std::is_trivial_v<T>
 [[nodiscard]] bool LayerQueue<T>::is_new_layer() const {
     return queue_begin_ == layer_begin_;
 }
 
-//template <typename T>
-//std::vector<T> LayerQueue<T>::layer_cases() const {
-//    std::vector<T> layer_cases;
-//    for (size_t offset = layer_begin_; offset < layer_end_; ++offset) {
-//        layer_cases.emplace_back(data_[offset]);
-//    }
-//    return layer_cases;
-//}
-
 template <typename T>
+requires std::is_trivial_v<T>
 std::vector<T> LayerQueue<T>::last_layer() const {
-    std::vector<T> layer;
-    layer.reserve(layer_end_ - layer_begin_);
-    for (auto offset = layer_begin_; offset < layer_end_; ++offset) {
-        layer.emplace_back(data_[offset]); // TODO: copy directly
-    }
-    return layer;
+    return {data_ + layer_begin_, data_ + layer_end_};
 }
 
 template <typename T>
+requires std::is_trivial_v<T>
 std::vector<std::vector<T>> LayerQueue<T>::all_layers() const {
     std::vector<std::vector<T>> result;
-    for (size_t i = 0; i < layers_.size() - 1; ++i) {
-        size_t begin = layers_[i];
-        size_t end = layers_[i + 1];
-
-        std::vector<T> layer {};
-        layer.reserve(end - begin);
-        for (auto offset = begin; offset < end; ++offset) {
-            layer.emplace_back(data_[offset]); // TODO: copy directly
-        }
+    for (size_t i = 0; i < layer_offset_.size() - 1; ++i) {
+        std::vector<T> layer {data_ + layer_offset_[i], data_ + layer_offset_[i + 1]};
         result.emplace_back(layer);
     }
     return result;
diff --git a/src/core/fast_cal/layer_queue.h b/src/core/fast_cal/layer_queue.h
index ffdc749..d92f723 100644
--- a/src/core/fast_cal/layer_queue.h
+++ b/src/core/fast_cal/layer_queue.h
@@ -7,12 +7,13 @@
 namespace klotski {
 
 template <typename T>
+requires std::is_trivial_v<T>
 class LayerQueue final {
 public:
     ~LayerQueue();
 
-    /// Construct from first layer cases and reserve size.
-    LayerQueue(std::initializer_list<T> first_layer, size_t reserve);
+    /// Construct from first layer nodes and reserve size.
+    LayerQueue(std::initializer_list<T> first_layer, size_t max_size);
 
     // ------------------------------------------------------------------------------------- //
 
@@ -44,14 +45,10 @@ public:
     // ------------------------------------------------------------------------------------- //
 
 private:
-    size_t layer_begin_, layer_end_;
-    size_t queue_begin_, queue_end_;
-
-    // std::vector<T> data_ {};
     T *data_ {nullptr};
-
-    std::vector<size_t> layers_ {};
-    // std::vector<std::pair<size_t, size_t>> layers_ {};
+    size_t layer_begin_ {0}, layer_end_;
+    size_t queue_begin_ {0}, queue_end_;
+    std::vector<size_t> layer_offset_ {0};
 };
 
 } // namespace klotski
diff --git a/src/core/main.cc b/src/core/main.cc
index b313b1c..5d59966 100644
--- a/src/core/main.cc
+++ b/src/core/main.cc
@@ -56,7 +56,7 @@ int main() {
     // }
 
     // for (auto x : fc.furthest()) {
-    //     std::cout << x << std::endl;
+    //     std::cout << x.to_common_code() << std::endl;
     // }
 
     fc.furthest();