using System;
using System.Linq;
 
public class Test
{
	public static void Main()
	{
        var arr = new[,] { { 3, 3, 3, 2, 1 },
                           { 2, 4, 3, 3, 3 },
                           { 3, 3, 4, 3, 1 },
                           { 2, 3, 5, 3, 1 } };
        int width = arr.GetLength(0), height = arr.GetLength(1), length = 3, value = 3;
        var h = Enumerable.Range(0, width)
                          .SelectMany(x => Enumerable.Range(0, height - length + 1)
                                                     .Select(y => Enumerable.Range(0, length)
                                                                            .Select(o => new { x, y = y + o }))
                                                     .Where(c => c.All(p => arr[p.x, p.y] == value))
                                                     .SelectMany(c => c));
        var v = Enumerable.Range(0, width - length + 1)
                          .SelectMany(x => Enumerable.Range(0, height)
                                                     .Select(y => Enumerable.Range(0, length)
                                                                            .Select(o => new { x = x + o, y }))
                                                     .Where(c => c.All(p => arr[p.x, p.y] == value))
                                                     .SelectMany(c => c));
        var all = h.Concat(v).Distinct();
        Console.WriteLine(string.Join("\n", all));
	}
}

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