diff --git a/src/klotski_core/common_code/common_code.h b/src/klotski_core/common_code/common_code.h
index e89ed3a..fbb45ea 100644
--- a/src/klotski_core/common_code/common_code.h
+++ b/src/klotski_core/common_code/common_code.h
@@ -127,3 +127,11 @@ inline bool operator==(const CommonCode &c1, const CommonCode &c2) noexcept { re
 inline bool operator!=(const CommonCode &c1, const CommonCode &c2) noexcept { return c1.unwrap() != c2.unwrap(); }
 
 } // namespace klotski
+
+/// In namespace std, let the CommonCode implement the standard hash function.
+template<>
+struct std::hash<klotski::CommonCode> {
+    inline std::size_t operator()(const klotski::CommonCode &common_code) const {
+        return static_cast<std::size_t>(common_code.unwrap());
+    }
+};
diff --git a/src/klotski_core/raw_code/raw_code.h b/src/klotski_core/raw_code/raw_code.h
index 7dbd306..605a912 100644
--- a/src/klotski_core/raw_code/raw_code.h
+++ b/src/klotski_core/raw_code/raw_code.h
@@ -116,3 +116,11 @@ inline bool operator==(const RawCode &r1, const RawCode &r2) noexcept { return r
 inline bool operator!=(const RawCode &r1, const RawCode &r2) noexcept { return r1.unwrap() != r2.unwrap(); }
 
 } // namespace klotski
+
+/// In namespace std, let the RawCode implement the standard hash function.
+template<>
+struct std::hash<klotski::RawCode> {
+    inline std::size_t operator()(const klotski::RawCode &raw_code) const {
+        return static_cast<std::size_t>(raw_code.unwrap());
+    }
+};
diff --git a/src/klotski_core/short_code/short_code.h b/src/klotski_core/short_code/short_code.h
index a8cdba4..8b8b978 100644
--- a/src/klotski_core/short_code/short_code.h
+++ b/src/klotski_core/short_code/short_code.h
@@ -141,3 +141,11 @@ inline bool operator==(const ShortCode &s1, const ShortCode &s2) noexcept { retu
 inline bool operator!=(const ShortCode &s1, const ShortCode &s2) noexcept { return s1.unwrap() != s2.unwrap(); }
 
 } // namespace klotski
+
+/// In namespace std, let the ShortCode implement the standard hash function.
+template<>
+struct std::hash<klotski::ShortCode> {
+    inline std::size_t operator()(const klotski::ShortCode &short_code) const {
+        return static_cast<std::size_t>(short_code.unwrap());
+    }
+};
diff --git a/test/codec/common_code.cc b/test/codec/common_code.cc
index d659e5a..acfdf53 100644
--- a/test/codec/common_code.cc
+++ b/test/codec/common_code.cc
@@ -1,5 +1,6 @@
 #include <thread>
 #include <algorithm>
+#include <unordered_set>
 #include "all_cases.h"
 #include "common_code.h"
 #include "gtest/gtest.h"
@@ -22,6 +23,11 @@ static inline void SHOULD_PANIC(const std::function<void()> &func) {
     EXPECT_EQ(panic_flag, true);
 }
 
+TEST(CommonCode, hash) {
+    auto tmp = std::unordered_set<CommonCode>{ CommonCode(TEST_CODE) };
+    EXPECT_EQ(tmp.size(), 1);
+}
+
 TEST(CommonCode, validity) {
     EXPECT_NE(CommonCode::check(0x3'A9'BF'0C'00), true); // invalid 2x2 block
     EXPECT_NE(CommonCode::check(0x1'D9'BF'0C'00), true); // invalid block range
diff --git a/test/codec/raw_code.cc b/test/codec/raw_code.cc
index 40c639d..ba721de 100644
--- a/test/codec/raw_code.cc
+++ b/test/codec/raw_code.cc
@@ -1,4 +1,5 @@
 #include <thread>
+#include <unordered_set>
 #include "raw_code.h"
 #include "all_cases.h"
 #include "gtest/gtest.h"
@@ -9,6 +10,11 @@ using klotski::CommonCode;
 
 const static uint64_t TEST_CODE = 0x0603'EDF5'CAFF'F5E2;
 
+TEST(RawCode, hash) {
+    auto tmp = std::unordered_set<RawCode>{ RawCode(TEST_CODE) };
+    EXPECT_EQ(tmp.size(), 1);
+}
+
 TEST(RawCode, validity) {
     EXPECT_EQ(RawCode::check(0x0A34'182B'3810'2D21), false); // invalid code
     EXPECT_EQ(RawCode::check(0x8603'EDF5'CAFF'F5E2), false); // high 4-bits not zero
diff --git a/test/codec/short_code.cc b/test/codec/short_code.cc
index 05932a7..878bc51 100644
--- a/test/codec/short_code.cc
+++ b/test/codec/short_code.cc
@@ -1,5 +1,6 @@
 #include <thread>
 #include <algorithm>
+#include <unordered_set>
 #include "all_cases.h"
 #include "short_code.h"
 #include "gtest/gtest.h"
@@ -22,6 +23,11 @@ static inline void SHOULD_PANIC(const std::function<void()> &func) {
     EXPECT_EQ(panic_flag, true);
 }
 
+TEST(ShortCode, hash) {
+    auto tmp = std::unordered_set<ShortCode>{ ShortCode(TEST_CODE) };
+    EXPECT_EQ(tmp.size(), 1);
+}
+
 TEST(ShortCode, validity) {
     EXPECT_NE(ShortCode::check(-1), true); // out of short code range
     EXPECT_NE(ShortCode::check(29670987), true); // out of short code range