using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        string seats = "xxoxoxoxoxoxooxxxxox";

        var results = seats.ToCharArray().GetSingles('o');

        foreach(var i in results)

        {

            Console.WriteLine(i);

        }

    }

}

public static class Ext

{

    public static IReadOnlyList<int> GetSingles<T>(this T[] source, T search)

    {

        var results = new List<int>();

        if(source.Length == 0)

        {

            return results;

        }

        if (source.Length == 1)

        {

            if (source[0].Equals(search))

            {

                results.Add(0);

            }

            return results;

        }

        if(source.Length >= 2)

        {

            if (source[0].Equals(search) && ! source[1].Equals(search))

            {

                results.Add(0);

            }

            if (source.Length == 2)

            {

                if (!source[0].Equals(search) && source[1].Equals(search))

                {

                    results.Add(1);

                }

                return results;

            }

        }

        ReadOnlySpan<T> window = new ReadOnlySpan<T>(source, 0, 3);

        int i = 1;

        for(; i < source.Length - 1; i++)

        {

            window = new ReadOnlySpan<T>(source, i - 1, 3);

            if(!window[0].Equals(search) && window[1].Equals(search) && !window[2].Equals(search))

            {

                results.Add(i);

            }

        }

        if(!window[1].Equals(search) && window[2].Equals(search))

        {

            results.Add(i + 1);

        }

        return results;

    }

}