using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        private static List<List<int>> cornerPossibilities = null;
        private static List<List<int>> trianglePossibilities = null;


        static void Main(string[] args)
        {
            SetupCornerPossibilities();
            SetupTrianglesPossibilities();

            var blocks = new List<bool> { false, true, false, true, true, false, false, false, false };

            var foundCorners = HasCornerPossibility(blocks);
            var foundTriangles = HasTrianglePossibility(blocks);

            if (foundCorners != null)
            {
                // do stuff 1
            }
            else if (foundTriangles != null)
            {
                // do stuff 2
            }
        }

        private static List<int> HasCornerPossibility(List<bool> blocks)
        {
            return HasPossibility(blocks, cornerPossibilities);
        }

        private static List<int> HasTrianglePossibility(List<bool> blocks)
        {
            return HasPossibility(blocks, trianglePossibilities);
        }

        private static List<int> HasPossibility(List<bool> blocks, List<List<int>> possibilities)
        {
            foreach (var possibility in cornerPossibilities)
            {
                var scopedBlocks = GetByIndexes(blocks, possibility);

                if (scopedBlocks.All(b => b))
                    return possibility;
            }

            return null;
        }

        private static IEnumerable<bool> GetByIndexes(List<bool> blocks, List<int> indexes)
        {
            // stackoverflow magic
            return blocks
                .Where((element, index) => indexes.Contains(index));
        }

        private static void SetupCornerPossibilities()
        {
            cornerPossibilities = new List<List<int>>
            {
                new List<int> { 1,3,4 },
                new List<int> { 3,4,6 },
                new List<int> { 4,5,7 }
            };
        }

        private static void SetupTrianglesPossibilities()
        {
            trianglePossibilities = new List<List<int>>
            {
                new List<int> { 7,3,1 },
                new List<int> { 3,7,5 },
                new List<int> { 3,1,5 },
                new List<int> { 1,5,7 }
            };
        }

    }
}