problems(cpp): add „393. UTF-8 Validation“

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/utf-8-validation.cpp

@@ -0,0 +1,121 @@
+#include <array>
+#include <exception>
+#include <iostream>
+#include <optional>
+#include <sstream>
+#include <string>
+#include <vector>
+
+namespace {
+class todo : public std::exception {
+    std::string cause;
+
+public:
+    todo()
+        : cause("Not yet implemented!")
+    {
+    }
+
+    todo(std::string&& excuse)
+        : cause("Not yet implemented: " + excuse)
+    {
+    }
+
+    virtual const char* what() const throw()
+    {
+        return cause.c_str();
+    }
+};
+
+auto expected_size(int first) -> std::optional<std::size_t> {
+    static constexpr std::array<int, 4> HEADERS = {
+        0, 6, 14, 30
+    };
+
+    for (auto i = 0; i < 4; i++) {
+        auto mask_length = 1 + i + (i > 0);
+        auto mask = (1 << (mask_length)) - 1;
+
+        if (((first >> (8 - mask_length)) & mask) == HEADERS[i]) {
+            return {i + 1};
+        }
+    }
+
+    return {};
+}
+
+}
+
+class Solution {
+    static constexpr int CONTINUATION_BYTE = 2;
+
+public:
+    auto validUtf8(const std::vector<int>& data) -> bool
+    {
+        for (auto i = 0; i < data.size();) {
+            auto expected_length = expected_size(data[i]);
+            if (!expected_length.has_value()) {
+                // std::cout << "corrupted first byte\n";
+                return false;
+            }
+
+            if (i + *expected_length > data.size()) {
+                // std::cout << "unexpected length of size " << data.size() << " ≠ " << *expected_length << "\n";
+                return false;
+            }
+
+            // check first byte
+            if (data[i] >= (1 << 8)) {
+                // std::cout << "incorrect leading byte" << "\n";
+                return false;
+            }
+
+            // check remaining bytes
+            for (auto j = 1; j < expected_length; j++) {
+                if ((data[i + j] >> 6) != CONTINUATION_BYTE) {
+                    // std::cout << "invalid continuation byte" << "\n";
+                    return false;
+                }
+            }
+
+            i += *expected_length;
+        }
+
+        return true;
+    }
+};
+
+#pragma region tests
+
+#include <gtest/gtest.h>
+
+TEST(examples, valid)
+{
+    Solution s;
+    ASSERT_TRUE(s.validUtf8(std::vector { 197, 130, 1 }));
+}
+
+TEST(examples, invalid)
+{
+    Solution s;
+    ASSERT_FALSE(s.validUtf8(std::vector { 235, 140, 4 }));
+}
+
+TEST(valid, ascii_byte)
+{
+    Solution s;
+    ASSERT_TRUE(s.validUtf8(std::vector { 64 }));
+}
+
+TEST(invalid, just_one_byte) {
+    Solution s;
+    ASSERT_FALSE(s.validUtf8(std::vector {2 << 7}));
+}
+
+int main(int argc, char** argv)
+{
+    ::testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}
+
+#pragma endregion /* tests */