diff --git a/src/fast_cal/cal_core.cc b/src/fast_cal/cal_core.cc
index 8753f6b..d2e1712 100644
--- a/src/fast_cal/cal_core.cc
+++ b/src/fast_cal/cal_core.cc
@@ -36,10 +36,20 @@ void FastCal::new_case(uint64_t code, uint64_t mask) {
     }).first->second);
 }
 
+/// build total search tree
+void FastCal::build(const RawCode &code) {
+    auto core = init((uint64_t)code);
+    /// start BFS search
+    while (!cache.empty()) {
+        core.next_cases(cache.front()->code, cache.front()->mask);
+        cache.pop();
+    }
+}
+
 /// found first matched target
 RawCode FastCal::target(const RawCode &code, const match_t &match) {
     auto core = init((uint64_t)code);
-    /// start bfs search
+    /// start BFS search
     while (!cache.empty()) {
         if (match(cache.front()->code)) {
             return RawCode::unsafe_create(cache.front()->code); // match target
@@ -55,7 +65,7 @@ std::vector<RawCode> FastCal::target_multi(const RawCode &code, const match_t &m
     auto core = init((uint64_t)code);
     auto layer_end = cache.back();
     std::vector<RawCode> matched; // matched list
-    /// start bfs search
+    /// start BFS search
     while (!cache.empty()) {
         if (match(cache.front()->code)) { // match target
             matched.emplace_back(cache.front()->code);
@@ -77,7 +87,7 @@ std::vector<RawCode> FastCal::furthest(const RawCode &code) {
     auto core = init((uint64_t)code);
     auto layer_end = cache.back();
     std::vector<RawCode> layer_cases;
-    /// start bfs search
+    /// start BFS search
     while (!cache.empty()) {
         core.next_cases(cache.front()->code, cache.front()->mask);
         layer_cases.emplace_back(
diff --git a/src/fast_cal/fast_cal.h b/src/fast_cal/fast_cal.h
index 6fbb844..a927aff 100644
--- a/src/fast_cal/fast_cal.h
+++ b/src/fast_cal/fast_cal.h
@@ -20,7 +20,7 @@ public:
     std::vector<RawCode> backtrack(const RawCode &code);
 
     /// BFS search functions
-    // TODO: build function with void return -> build total tree
+    void build(const RawCode &code);
     RawCode solve(const RawCode &code);
     std::vector<RawCode> furthest(const RawCode &code);
     std::vector<RawCode> solve_multi(const RawCode &code);
diff --git a/src/main.cc b/src/main.cc
index 354915a..97fa75c 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -25,7 +25,8 @@ int main() {
 
 //    AllCases::build();
 
-//    auto f = FastCal();
+    auto f = FastCal();
+    f.build(RawCode::from_common_code("1a9bf0c"));
 //    auto ret = f.solve(RawCode::from_common_code("1a9bf0c"));
 
 //    auto ret = f.target(RawCode::from_common_code("1a9bf0c"), [](uint64_t code) {
@@ -44,9 +45,9 @@ int main() {
 //        std::cout << "step number: " << f.step_num(ret) << std::endl;
 //    }
 
-    for (const auto &c : FastCal::resolve(RawCode::from_common_code("1a9bf0c"))) {
+//    for (const auto &c : FastCal::resolve(RawCode::from_common_code("1a9bf0c"))) {
 //        std::cout << c << std::endl;
-    }
+//    }
 
 //    for (const auto &s : FastCal::to_furthest(RawCode::from_common_code("1a9bf0c"))) {
 //        for (const auto &c : s) {