AorB - HackerRank C# - study code #6 - BigInteger - try the class yourself

AorB_studyCsharp_ex6.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Numerics;

class Solution
{
    static void Main(String[] args)
    {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution */
        byte[] lookup = new byte[256];
        for (int i = 0; i < lookup.Length; i++)
        {
            byte sum = 0;
            int temp = i;
            while (temp > 0)
            {
                sum += (byte)(temp % 2);
                temp >>= 1;
            }
            lookup[i] = sum;
        }

        int t = Convert.ToInt32(Console.ReadLine());
        for (int a0 = 0; a0 < t; a0++)
        {
            int k = Convert.ToInt32(Console.ReadLine());
            BigInteger A = ReadHex();
            BigInteger B = ReadHex();
            BigInteger C = ReadHex();

            BigInteger A2 = A & C;
            BigInteger A3 = A2 ^ A;

            BigInteger B2 = B & C;
            BigInteger B3 = B2 ^ B;

            BigInteger C2 = ((C ^ A2) | B2) ^ B2;
            
            foreach (byte b in A3.ToByteArray())
            {
                k -= lookup[b];
            }
            foreach (byte b in B3.ToByteArray())
            {
                k -= lookup[b];
            }
            foreach (byte b in C2.ToByteArray())
            {
                k -= lookup[b];
            }
            
            if (k < 0)
                Console.WriteLine(-1);
            else
            {
                A2 = A - A3;
                B2 = B - B3 + C2;

                C2 = A2 & B2;
                byte[] Ab = A2.ToByteArray();
                byte[] Bb = B2.ToByteArray();
                byte[] Ra, Rb;
                byte[] bit = { 128, 64, 32, 16, 8, 4, 2, 1 };
                if (Ab.Length > Bb.Length)
                {
                    Ra = Ab;
                    Rb = new byte[Ab.Length];
                    Array.Copy(Bb, 0, Rb, 0, Bb.Length);
                }
                else
                {
                    Rb = Bb;
                    Ra = new byte[Bb.Length];
                    Array.Copy(Ab, 0, Ra, 0, Ab.Length);
                }

                for (int i = Ra.Length - 1; i >= 0; i--)
                {
                    for (int j = 0; j < 8; j++)
                    {
                        if (k == 0)
                            break;

                        if ((Ra[i] & bit[j]) == 0)
                        {
                            continue;
                        }
                        else if ((Ra[i] & bit[j]) == (Rb[i] & bit[j]))
                        {
                            Ra[i] -= bit[j];
                            k--;
                        }
                        else if ((Ra[i] & bit[j]) == bit[j]
                            && (Rb[i] & bit[j]) == 0
                            && k > 1)
                        {
                            Ra[i] -= bit[j];
                            Rb[i] += bit[j];
                            k -= 2;
                        }
                    }
                    if (k == 0)
                        break;
                }

                PrintHex(Ra);
                PrintHex(Rb);
            }
        }
    }

    static void PrintHex(byte[] s)
    {
        bool firstDigit = true;
        for (int i = s.Length-1; i >= 0; i--)
        {
            if (s[i] == 0 && firstDigit)
                continue;
            string s2 = Convert.ToString(s[i], 16).ToUpper();
            if (s2.Length == 1 && !firstDigit)
                s2 = "0" + s2;
            firstDigit = false;
            Console.Write(s2);
        }
        if (firstDigit)
            Console.Write("0");
        Console.WriteLine();
    }

    static BigInteger ReadHex()
    {
        string S = Console.ReadLine();
        if(S.Length % 2 == 1)
        {
            S = "0" + S;
        }
        else
        {
            S = "00" + S;
        }
        char[] T = S.ToCharArray();
        byte[] B = new byte[T.Length / 2];
        for (int i = 0; i < T.Length; i += 2)
        {
            B[B.Length - i / 2 - 1] = Convert.ToByte(T[i] + "" + T[i + 1], 16);
        }
        return new BigInteger(B);
    }
}