diff --git a/src/analyse/analyse.h b/src/analyse/analyse.h
index 2cb1fb5..f8a330d 100644
--- a/src/analyse/analyse.h
+++ b/src/analyse/analyse.h
@@ -43,6 +43,7 @@ private:
     void new_case(uint64_t code, uint64_t mask);
 
 
+/// backtrack definitions
 public:
     struct backtrack_t {
         uint64_t code;
@@ -50,20 +51,9 @@ public:
         std::list<backtrack_t*> last;
         std::list<backtrack_t*> next;
     };
+    typedef std::vector<std::unordered_map<uint64_t, backtrack_t>> backtrack_data_t;
 
-    void backtrack_demo(const std::vector<uint64_t> &codes);
-
-    /// backtrack definitions
-
-//    struct backtrack_t {
-//        uint64_t code;
-//        uint32_t layer_num;
-//        uint32_t layer_index;
-//        std::list<backtrack_t*> next;
-//    };
-
-    // TODO: backtrack for multi-codes
-//    void backtrack(uint64_t code);
-//    void backtrack(const std::vector<uint64_t> &raw_code_list);
+    // TODO: try using unordered_set
+    backtrack_data_t backtrack_demo(const std::vector<uint64_t> &codes);
 
 };
diff --git a/src/analyse/backtrack.cc b/src/analyse/backtrack.cc
index 5b7422a..1e88fd7 100644
--- a/src/analyse/backtrack.cc
+++ b/src/analyse/backtrack.cc
@@ -1,104 +1,52 @@
+#include <algorithm>
 #include "analyse.h"
 
 #include <iostream>
 
-#include <set>
-#include <unordered_set>
-
-#include <algorithm>
-
-#include "common_code.h"
-
-// TODO: using const RawCode& instead of uint64_t
-
-//namespace std {
-//    template<>
-//    struct hash<Analyse::backtrack_t> {
-//        std::size_t operator()(const Analyse::backtrack_t &b) const {
-//            std::cout << "get hash: " << b.code << std::endl;
-//            return std::hash<uint64_t>()(b.code);
-//        }
-//    };
-//
-//    template<>
-//    struct equal_to<Analyse::backtrack_t> {
-//        bool operator()(const Analyse::backtrack_t &b1, const Analyse::backtrack_t &b2) const {
-//            std::cout << "get eq: " << b1.code << " ? " << b2.code << std::endl;
-//            return b1.code == b2.code;
-//        }
-//    };
-//}
-
-void Analyse::backtrack_demo(const std::vector<uint64_t> &codes) {
-
-
+Analyse::backtrack_data_t Analyse::backtrack_demo(const std::vector<uint64_t> &codes) {
+    /// codes pre-check and sort by steps
     std::vector<std::vector<analyse_t*>> todos;
-
     for (const auto &code : codes) {
-
         auto c = cases.find(code);
-
-        if (c == cases.end()) {
-            // TODO: invalid input
-            return;
+        if (c == cases.end()) { // invalid input
+            return backtrack_data_t{}; // return empty data
         }
-
         if (c->second.step >= todos.size()) {
-            todos.resize(c->second.step + 1);
+            todos.resize(c->second.step + 1); // enlarge schedule list
         }
-
         todos[c->second.step].emplace_back(&c->second);
-
     }
-
-    std::reverse(todos.begin(), todos.end());
-
+    std::reverse(todos.begin(), todos.end()); // backtrack start from further layer
 
     struct cache_t {
         analyse_t *a;
         backtrack_t *b;
     };
-
     std::queue<cache_t> track_cache;
-    std::vector<std::unordered_map<uint64_t, backtrack_t>> track_data;
-
-//    track_data.resize(82); // TODO: setting as (max steps + 1)
-
-    track_data.resize(todos.size());
-
-    // TODO: for diff layer cases, layer_num from big to small -> if found then skip search
-
+    Analyse::backtrack_data_t track_data(todos.size());
+    /// start backtrack process
     for (const auto &todo : todos) {
-
         if (todo.empty()) {
-            continue;
+            continue; // without scheduled cases
         }
-
-        /// clear track cache
-        std::queue<cache_t>{}.swap(track_cache);
-
+        std::queue<cache_t>{}.swap(track_cache); // clear track cache
         for (const auto c : todo) {
-
-            // TODO: if c already exist -> skip
+            /// case already exist -> skip its backtrack
             if (track_data[c->step].find(c->code) == track_data[c->step].end()) {
-
                 track_cache.emplace(cache_t{
                     .a = c,
                     .b = &track_data[c->step].emplace(c->code, backtrack_t{
                         .code = c->code,
                         .layer_num = c->step,
-                        .last = std::list<backtrack_t *>{},
-                        .next = std::list<backtrack_t *>{},
+                        .last = std::list<backtrack_t *>{}, // without parent node
+                        .next = std::list<backtrack_t *>{}, // without sub node
                     }).first->second,
                 });
             }
-
         }
-
-
+        /// backtrack until root case
         while (!track_cache.empty()) {
-            /// handle first element and pop it
-            auto curr = track_cache.front();
+            auto curr = track_cache.front(); // handle first element
             for (auto src : curr.a->src) { // traverse src cases of current node
                 auto t_src = track_data[src->step].find(src->code);
                 if (t_src != track_data[src->step].end()) { // match src case
@@ -123,8 +71,6 @@ void Analyse::backtrack_demo(const std::vector<uint64_t> &codes) {
             }
             track_cache.pop();
         }
-
-
     }
 
 
@@ -152,4 +98,6 @@ void Analyse::backtrack_demo(const std::vector<uint64_t> &codes) {
     }
 
 
+    return track_data;
+
 }