LeetCode/problems/utf-8-validation.cpp

#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 */