probability

gistfile1.cs

class Solution
{
  static void Main(String[] args)
	{
    var t = long.Parse(Console.ReadLine());
		for (var tt = 0; tt < t; tt++)
		{
			var s = Console.ReadLine();
			var k = int.Parse(s.Split()[1]);
			s = Console.ReadLine();
			var n = s.Length;
			var arr = new long[n];
			var count = 0L;
			var ones = 0L;
			for (var a = 0; a < n; a++)
			{
				if (s[a] == '1')
				{
					ones++;
					count += ones;
					if (a - k > 0)
					{
						count -= arr[a - k - 1];
					}
				}
				arr[a] = ones;
			}
			
			count = count * 2 - arr[arr.Length - 1];
			
			long nn = (long)n * n;
			var gcd = Gcd(nn, count);
			
			Console.Write(count / gcd);
			Console.Write('/');
			Console.WriteLine(nn / gcd);
		}
    }
	
	private static long Gcd(long a, long b)
	{
		while (b != 0)
			b = a % (a = b);
		return a;
	}
}