Solution

CMakeLists.txt

@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.21)
+project(clock_numbers)
+
+set(CMAKE_CXX_STANDARD 14)
+
+add_executable(clock_numbers main.cpp)

main.cpp

@@ -0,0 +1,86 @@
+#include <iostream>
+#include <array>
+#include <functional>
+#include <unordered_set>
+
+typedef union {
+    struct {
+        uint8_t hours_tens;
+        uint8_t hours_ones;
+        uint8_t minutes_tens;
+        uint8_t minutes_ones;
+    } clk;
+    uint32_t data;
+} clk_t;
+
+template<>
+struct std::hash<clk_t> {
+    std::size_t operator()(clk_t const &clk) const noexcept {
+        return clk.data;
+    }
+};
+
+template<>
+struct std::equal_to<clk_t> {
+    bool operator()(clk_t const &lhs, clk_t const &rhs) const noexcept {
+        return lhs.data == rhs.data;
+    }
+};
+
+bool is_clock_valid(clk_t const &clk) {
+
+    auto hours_tens = clk.clk.hours_tens;
+    if (hours_tens > 2) {
+        return false;
+    }
+
+    auto hours_ones = clk.clk.hours_ones;
+    if (hours_tens == 2 && hours_ones > 3) {
+        return false;
+    }
+
+    auto minutes_tens = clk.clk.minutes_tens;
+    if (minutes_tens > 5) {
+        return false;
+    }
+
+    return true;
+}
+
+int solution(int A, int B, int C, int D) {
+
+    uint8_t a = A, b = B, c = C, d = D;
+    std::unordered_set<clk_t> uniqs = {
+            {a, b, c, d},
+            {a, b, d, c},
+            {a, c, b, d},
+            {a, c, d, b},
+            {a, d, b, c},
+            {a, d, c, b},
+            {b, a, c, d},
+            {b, a, d, c},
+            {b, c, a, d},
+            {b, c, d, a},
+            {b, d, a, c},
+            {b, d, c, a},
+            {c, a, b, d},
+            {c, a, d, b},
+            {c, b, a, d},
+            {c, b, d, a},
+            {c, d, a, b},
+            {c, d, b, a},
+            {d, a, b, c},
+            {d, a, c, b},
+            {d, b, a, c},
+            {d, b, c, a},
+            {d, c, a, b},
+            {d, c, b, a},
+    };
+
+    return std::count_if(uniqs.begin(), uniqs.end(), is_clock_valid);
+}
+
+int main() {
+    std::cout << solution(2, 3, 3, 2) << std::endl;
+    return 0;
+}