AorB - HackerRank - world sprint - study code C#

AorB_studyCsharp_A2.cs

using System;
using System.Collections.Generic;
using System.IO;
class Solution
{
    static void Main(String[] args)
    {
        new A_or_B().Solve();
    }
}

class A_or_B
{
	public void Solve()
	{
		var n = int.Parse(Console.ReadLine());

		while (--n >= 0)
		{
			var k = int.Parse(Console.ReadLine());
			var a = ToBits(Console.ReadLine());
			var b = ToBits(Console.ReadLine());
			var c = ToBits(Console.ReadLine());

			if (!Modify(k, a, b, c))
			{
				Console.WriteLine(-1);
			}
			else
			{
				Console.WriteLine(ToString(a));
				Console.WriteLine(ToString(b));
			}
		}
	}

	string ToString(int[] a)
	{
		var c = "0123456789ABCDEF";
		var s = new char[a.Length >> 2];
		var j = 0;

		for (var i = 0; i < a.Length; i += 4)
		{
			s[i >> 2] = c[(a[i] << 3) | (a[i + 1] << 2) | (a[i + 2] << 1) | (a[i + 3])];
		}

		for (; j + 1 < s.Length && s[j] == '0'; ++j) ;

		return new string(s, j, s.Length - j);
	}

	bool Modify(int k, int[] a, int[] b, int[] c)
	{
		var n = a.Length;

		for (var i = 0; i < n; ++i)
		{
			if (c[i] == 0)
			{
				if (a[i] == 1)
				{
					if (k == 0)
					{
						return false;
					}

					a[i] = 0;
					--k;
				}

				if (b[i] == 1)
				{
					if (k == 0)
					{
						return false;
					}

					b[i] = 0;
					--k;
				}
			}
			else if (a[i] == 0 && b[i] == 0)
			{
				if (k == 0)
				{
					return false;
				}

				b[i] = 1;
				--k;
			}
		}

		for (var i = 0; i < n && k > 0; ++i)
		{
			if (a[i] == 1)
			{
				if (b[i] == 1)
				{
					a[i] = 0;
					--k;
				}
				else if (k > 1)
				{
					a[i] = 0;
					b[i] = 1;
					k -= 2;
				}
			}
		}

		return true;
	}

	int[] ToBits(string s)
	{
		var a = new int[200004];

		for (int i = 0, j = a.Length - 4 * s.Length; i < s.Length; ++i, j += 4)
		{
			switch (s[i])
			{
				case '0':
				{
					break;
				}
				case '1':
				{
					a[j + 3] = 1;
					break;
				}
				case '2':
				{
					a[j + 2] = 1;
					break;
				}
				case '3':
				{
					a[j + 2] = 1;
					a[j + 3] = 1;
					break;
				}
				case '4':
				{
					a[j + 1] = 1;
					break;
				}
				case '5':
				{
					a[j + 1] = 1;
					a[j + 3] = 1;
					break;
				}
				case '6':
				{
					a[j + 1] = 1;
					a[j + 2] = 1;
					break;
				}
				case '7':
				{
					a[j + 1] = 1;
					a[j + 2] = 1;
					a[j + 3] = 1;
					break;
				}
				case '8':
				{
					a[j + 0] = 1;
					break;
				}
				case '9':
				{
					a[j + 0] = 1;
					a[j + 3] = 1;
					break;
				}
				case 'A':
				{
					a[j + 0] = 1;
					a[j + 2] = 1;
					break;
				}
				case 'B':
				{
					a[j + 0] = 1;
					a[j + 2] = 1;
					a[j + 3] = 1;
					break;
				}
				case 'C':
				{
					a[j + 0] = 1;
					a[j + 1] = 1;
					break;
				}
				case 'D':
				{
					a[j + 0] = 1;
					a[j + 1] = 1;
					a[j + 3] = 1;
					break;
				}
				case 'E':
				{
					a[j + 0] = 1;
					a[j + 1] = 1;
					a[j + 2] = 1;
					break;
				}
				case 'F':
				{
					a[j + 0] = 1;
					a[j + 1] = 1;
					a[j + 2] = 1;
					a[j + 3] = 1;
					break;
				}
				default:
				{
					Console.WriteLine(s[i]);
					throw new Exception("" + s[i]);
				}
			}
		}

		return a;
	}
}