diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1f1d669..b19eee3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,4 +3,5 @@ set(CMAKE_CXX_STANDARD 14)
 project(klotski)
 
 #add_subdirectory(src)
-add_subdirectory(all_cases)
+#add_subdirectory(all_cases)
+add_subdirectory(klotski)
diff --git a/klotski/CMakeLists.txt b/klotski/CMakeLists.txt
new file mode 100644
index 0000000..ba0fdf1
--- /dev/null
+++ b/klotski/CMakeLists.txt
@@ -0,0 +1,4 @@
+cmake_minimum_required(VERSION 3.0)
+set(CMAKE_CXX_STANDARD 14)
+
+add_executable(klotski main.cc common.cc all_cases.cc)
diff --git a/klotski/all_cases.cc b/klotski/all_cases.cc
new file mode 100644
index 0000000..3b2ee2f
--- /dev/null
+++ b/klotski/all_cases.cc
@@ -0,0 +1,98 @@
+#include <algorithm>
+#include "common.h"
+#include "all_cases.h"
+
+inline uint32_t binary_count(uint32_t bin) { // get number of non-zero bits
+    bin -= (bin >> 1) & 0x55555555;
+    bin = (bin & 0x33333333) + ((bin >> 2) & 0x33333333);
+    bin = ((bin >> 4) + bin) & 0x0F0F0F0F;
+//    return (bin * 0x01010101) >> 24; // AMD CPU
+    bin += bin >> 8;
+    bin += bin >> 16;
+    return bin & 0b111111;
+}
+
+void AllCases::generate_ranges(int n1, int n2, int n3, int n4) { // generate target ranges
+    int len, limit;
+    constexpr uint32_t M_01 = 0b01 << 30;
+    constexpr uint32_t M_10 = 0b10 << 30;
+    constexpr uint32_t M_11 = 0b11 << 30;
+    std::vector<uint32_t> cache_1, cache_2;
+
+    len = n1 + n2;
+    limit = 0b1 << len;
+    for (uint32_t bin = 0; bin < limit; ++bin) {
+        if (binary_count(bin) != n2) { // skip binary without `n2` non-zero bits
+            continue;
+        }
+        uint32_t range = 0;
+        for (int i = 0; i < len; ++i) { // generate range base on binary value
+            range >>= 2;
+            if ((bin >> i) & 0b1) { // non-zero bit
+                range |= M_01; // 01000...
+            }
+        }
+        cache_1.emplace_back(range); // insert into first layer
+    }
+
+    len += n3;
+    limit <<= n3;
+    for (uint32_t bin = 0; bin < limit; ++bin) {
+        if (binary_count(bin) != n3) { // skip binary without `n3` non-zero bits
+            continue;
+        }
+        for (uint32_t base : cache_1) { // traverse first layer
+            uint32_t range = 0;
+            for (int i = 0; i < len; ++i) { // generate range base on binary value
+                if ((bin >> i) & 0b1) { // non-zero bit
+                    (range >>= 2) |= M_10; // 10000...
+                    continue;
+                }
+                (range >>= 2) |= base & M_11;
+                base <<= 2;
+            }
+            cache_2.emplace_back(range); // insert into second layer
+        }
+    }
+
+    len += n4;
+    limit <<= n4;
+    for (uint32_t bin = 0; bin < limit; ++bin) {
+        if (binary_count(bin) != n4) { // skip binary without `n4` non-zero bits
+            continue;
+        }
+        for (uint32_t base : cache_2) { // traverse second layer
+            uint32_t range = 0;
+            for (int i = 0; i < len; ++i) { // generate range base on binary value
+                if ((bin >> i) & 0b1) { // non-zero bit
+                    (range >>= 2) |= M_11; // 11000...
+                    continue;
+                }
+                (range >>= 2) |= base & M_11;
+                base <<= 2;
+            }
+            basic_ranges.emplace_back(range); // insert into release ranges
+        }
+    }
+}
+
+void AllCases::build_basic_ranges() { // build basic ranges
+    for (int n = 0; n <= 7; ++n) { // number of 1x2 and 2x1 block -> 0 ~ 7
+        for (int n_2x1 = 0; n_2x1 <= n; ++n_2x1) { // number of 2x1 block -> 0 ~ n
+            for (int n_1x1 = 0; n_1x1 <= (14 - n * 2); ++n_1x1) { // number of 1x1 block -> 0 ~ (14 - 2n)
+                int n_1x2 = n - n_2x1;
+                int n_space = 16 - n * 2 - n_1x1;
+                /// 0x0 -> 00 | 1x2 -> 01 | 2x1 -> 10 | 1x1 -> 11
+                generate_ranges(n_space, n_1x2, n_2x1, n_1x1); // generate target ranges
+            }
+        }
+    }
+    std::sort(basic_ranges.begin(), basic_ranges.end()); // sort basic ranges
+    for (uint32_t &range : basic_ranges) {
+        range = Common::range_reverse(range); // range reverse
+    }
+}
+
+const std::vector<uint32_t>* AllCases::get_basic_ranges() {
+    return &basic_ranges;
+}
diff --git a/klotski/all_cases.h b/klotski/all_cases.h
new file mode 100644
index 0000000..e2ada86
--- /dev/null
+++ b/klotski/all_cases.h
@@ -0,0 +1,21 @@
+#pragma once
+
+#include <vector>
+#include <cstdint>
+
+class AllCases {
+public:
+//    AllCases() {}
+//    void find_all_cases();
+
+    void build_basic_ranges();
+
+    const std::vector<uint32_t>* get_basic_ranges();
+
+private:
+//    std::vector<uint32_t> all_cases[16];
+    std::vector<uint32_t> basic_ranges;
+
+//    void load_basic_ranges();
+    void generate_ranges(int n1, int n2, int n3, int n4);
+};
diff --git a/klotski/common.cc b/klotski/common.cc
new file mode 100644
index 0000000..21a2118
--- /dev/null
+++ b/klotski/common.cc
@@ -0,0 +1,40 @@
+#include "common.h"
+
+uint32_t Common::range_reverse(uint32_t bin) { // reverse binary every 2-bits
+    bin = ((bin << 16) & 0xFFFF0000) | ((bin >> 16) & 0x0000FFFF);
+    bin = ((bin << 8) & 0xFF00FF00) | ((bin >> 8) & 0x00FF00FF);
+    bin = ((bin << 4) & 0xF0F0F0F0) | ((bin >> 4) & 0x0F0F0F0F);
+    return ((bin << 2) & 0xCCCCCCCC) | ((bin >> 2) & 0x33333333);
+}
+
+bool Common::check_case(uint32_t head, uint32_t range) { // check whether the case is valid
+    uint32_t mask = 0b110011 << head; // fill 2x2 block
+    for (int addr = 0; range; range >>= 2) { // traverse every 2-bits
+        while (mask >> addr & 0b1) {
+            ++addr; // search next not filled block
+        }
+        switch (range & 0b11) {
+            case 0b00: // space block
+            case 0b11: // 1x1 block
+                if (addr > 19) { // invalid address
+                    return false;
+                }
+                mask |= 0b1 << addr; // fill 1x1 block
+                break;
+            case 0b10: // 2x1 block
+                if (addr > 15 || mask >> (addr + 4) & 0b1) { // invalid address
+                    return false;
+                }
+                mask |= 0b10001 << addr; // fill 2x1 block
+                break;
+            case 0b01: // 1x2 block
+                if (addr > 18 || (addr & 0b11) == 0b11 || mask >> (addr + 1) & 0b1) { // invalid address
+                    return false;
+                }
+                mask |= 0b11 << addr; // fill 1x2 block
+                break;
+        }
+        // TODO: should we ensure that low-bits as 0?
+    }
+    return true; // valid case
+}
diff --git a/klotski/common.h b/klotski/common.h
new file mode 100644
index 0000000..8c80a6c
--- /dev/null
+++ b/klotski/common.h
@@ -0,0 +1,9 @@
+#pragma once
+
+#include <cstdint>
+
+class Common {
+public:
+    static uint32_t range_reverse(uint32_t bin);
+    static bool check_case(uint32_t head, uint32_t range);
+};
diff --git a/klotski/main.cc b/klotski/main.cc
new file mode 100644
index 0000000..52e02e4
--- /dev/null
+++ b/klotski/main.cc
@@ -0,0 +1,13 @@
+#include <iostream>
+#include "all_cases.h"
+
+int main() {
+
+    auto a = AllCases();
+    a.build_basic_ranges();
+
+    auto br = a.get_basic_ranges();
+    std::cout << br->size() << std::endl;
+
+    return 0;
+}