/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
Write your code in this editor and press "Run" button to compile and execute it.

*******************************************************************************/

#include <iostream>
#include <cstring>
#include <cstdint>
#include <algorithm>

using namespace std;

constexpr int8_t kHexDigits[256] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  -1, -1, -1, -1, -1, -1, -1, 10, 11, 12, 13, 14, 15, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
};

inline int8_t HexToInt(char c)
{
  return kHexDigits[uint8_t(c)];
}

inline bool IsValidHex(std::string s)
{
  return std::all_of(s.begin(), s.end(), [](char c) { return HexToInt(c) != -1; });
}

/**
 * Converts a hexadecimal to binary format if the hex string will fit the buffer.
 * Smaller hex strings are left padded with zeroes.
 */
inline bool HexToBinary(std::string hex, uint8_t *buffer, size_t buffer_size)
{
  memset(buffer, 0, buffer_size);

  if (hex.size() > buffer_size * 2)
  {
    return false;
  }

  int64_t hex_size     = int64_t(hex.size());
  int64_t buffer_pos   = int64_t(buffer_size) - (hex_size + 1) / 2;
  int64_t last_hex_pos = hex_size - 1;

  int64_t i = 0;
  for (; i < last_hex_pos; i += 2)
  {
    buffer[buffer_pos++] = (HexToInt(hex[i]) << 4) | HexToInt(hex[i + 1]);
  }

  if (i == last_hex_pos)
  {
    buffer[buffer_pos] = HexToInt(hex[i]);
  }

  return true;
}

inline bool HexToBinaryFixed(std::string hex, uint8_t *buffer, size_t buffer_size)
{
  memset(buffer, 0, buffer_size);

  if (hex.size() > buffer_size * 2)
  {
    return false;
  }

  int64_t hex_size     = int64_t(hex.size());
  int64_t buffer_pos   = int64_t(buffer_size) - (hex_size + 1) / 2;
  int64_t last_hex_pos = hex_size - 1;
  
  bool is_hex_size_odd = (hex_size % 2) == 1;
  int64_t i = 0;

  if (is_hex_size_odd)
  {
    buffer[buffer_pos++] = HexToInt(hex[i++]);
  }

  for (; i < last_hex_pos; i += 2)
  {
    buffer[buffer_pos++] = (HexToInt(hex[i]) << 4) | HexToInt(hex[i + 1]);
  }

  return true;
}

int main()
{
    std::string trace_id_hex = "78cfcfec62ae9e9";
    uint8_t trace_id[16];
    HexToBinary(trace_id_hex, trace_id, sizeof(trace_id));
    
    uint8_t trace_id_fix[16];
    HexToBinaryFixed(trace_id_hex, trace_id_fix, sizeof(trace_id));
    cout<<"Hello World";

    return 0;
}