diff --git a/src/fast_cal/fast_cal.cc b/src/fast_cal/fast_cal.cc
index 7a0d180..42c7b8f 100644
--- a/src/fast_cal/fast_cal.cc
+++ b/src/fast_cal/fast_cal.cc
@@ -1,12 +1,10 @@
+#include <algorithm>
 #include "core.h"
 #include "common.h"
 #include "fast_cal.h"
-
 #include "raw_code.h"
 
-#include <iostream>
-#include <algorithm>
-
+/// klotski resolved -> 2x2 block at address 13 (aka 0xD)
 RawCode FastCal::solve(RawCode code) {
     return FastCal::target(code, [](uint64_t code) {
         return ((code >> (3 * 0xD)) & 0b111) == B_2x2; // check 2x2 block address
@@ -19,34 +17,31 @@ std::vector<RawCode> FastCal::solve_multi(RawCode code) {
     });
 }
 
-std::vector<uint64_t> FastCal::backtrack(uint64_t code) {
-    std::vector<uint64_t> path;
-
-    // TODO: confirm code exist
-    auto node = &cases[code];
-
-    while (node != nullptr) {
-        path.emplace_back(node->code);
-        node = node->last;
+/// backtrack of FastCal tree
+int FastCal::step_num(RawCode code) {
+    auto tmp = cases.find((uint64_t)code);
+    if (tmp == cases.end()) {
+        return -1; // code not exist
     }
-
-    std::reverse(path.begin(), path.end());
-    return path;
-
-}
-
-
-
-uint32_t FastCal::step_num(uint64_t code) {
-
-    uint32_t num = 0;
-
-    // TODO: confirm code exist
-    auto node = &cases[code];
-
+    int num = 0; // step number
+    auto node = &tmp->second; // backtrack entry
     while ((node = node->last) != nullptr) {
         ++num;
     }
-
     return num;
 }
+
+std::vector<RawCode> FastCal::backtrack(RawCode code) {
+    auto tmp = cases.find((uint64_t)code);
+    if (tmp == cases.end()) {
+        return std::vector<RawCode>{}; // code not exist
+    }
+    auto node = &tmp->second; // backtrack entry
+    std::vector<RawCode> path; // backtrack path
+    while (node != nullptr) {
+        path.emplace_back(RawCode::unsafe_create(node->code)); // record path info
+        node = node->last;
+    }
+    std::reverse(path.begin(), path.end()); // reverse path cases
+    return path;
+}
diff --git a/src/fast_cal/fast_cal.h b/src/fast_cal/fast_cal.h
index 50e72e7..395745b 100644
--- a/src/fast_cal/fast_cal.h
+++ b/src/fast_cal/fast_cal.h
@@ -15,7 +15,9 @@ class FastCal {
 public:
     typedef std::function<bool(uint64_t)> match_t;
 
-    /// xxx_multi only search until same layer
+    /// backtrack functions
+    int step_num(RawCode code);
+    std::vector<RawCode> backtrack(RawCode code);
 
     /// BFS search functions
     RawCode solve(RawCode code);
@@ -25,15 +27,11 @@ public:
     std::vector<RawCode> target_multi(RawCode code, const match_t &match);
 
 
+    // TODO: static search functions
 
     // TODO: search / search_multi / resolve / resolve_multi
     // TODO: static furthest function
 
-    std::vector<uint64_t> backtrack(uint64_t code);
-
-    uint32_t step_num(uint64_t code);
-
-    // TODO: static search functions
 
 
 private:
diff --git a/src/main.cc b/src/main.cc
index 0b1dad2..6eaf102 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -28,12 +28,21 @@ int main() {
     auto f = FastCal();
 //    auto ret = f.solve((uint64_t)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) {
+//        return code == (uint64_t)RawCode::from_common_code(0xDB23B6C00);
+//        return code == 0x0FFB5E7E5AEC741A;
+//    });
+
 //    auto ret = f.solve(RawCode::from_common_code("1aaef0c"));
 
     if (ret == FC_NOT_FOUND) {
         std::cout << "not found" << std::endl;
     } else {
-        std::cout << ret << std::endl;
+        for (const auto &r : f.backtrack(ret)) {
+            std::cout << r << std::endl;
+        }
+        std::cout << "step number: " << f.step_num(ret) << std::endl;
     }
 
 //    std::cout << f.step_num(ret) << std::endl;