update: short code offset header

src/klotski_core/short_code/offset/all_cases_offset.h

@@ -1,12 +1,18 @@
 #pragma once
 
+/// This is the head index, the offset (0 ~ 29334498) in all cases is obtained
+/// according to the `head` (0 ~ 15). In other words, the short code range can be
+/// obtained according to the position of the 2x2 block.
+
 #include <cstdint>
 
 namespace klotski {
-    const uint32_t ALL_CASES_OFFSET[16] = {
-               0,  2942906,  5203298,  8146204,
-         8146204, 10468254, 12345199, 14667249,
-        14667249, 16989299, 18866244, 21188294,
-        21188294, 24131200, 26391592, 29334498,
-    };
-}
+
+const uint32_t ALL_CASES_OFFSET[16] = {
+           0,  2942906,  5203298,  8146204,
+     8146204, 10468254, 12345199, 14667249,
+    14667249, 16989299, 18866244, 21188294,
+    21188294, 24131200, 26391592, 29334498,
+};
+
+} // namespace klotski