const f = x => ( (x.toString().includes('.')) ? (x.toString().split('.').pop().length) : (0) );

f(123); // 0
f(123.456); // 3

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
	public static void Main()
	{
		var a = new[] { 1, 1, 2, 3, 3, 4, 4, 5 };
		var r = a.Where(x => a.Count(n => n == x) > 1).Distinct();
		
		foreach (var item in r)
		{
			Console.WriteLine(item);
		}
	}
}

const random = (min, max) => Math.floor(Math.random() * (max - min) + min),

offerTitles = [
	"Большая уютная квартира",
	"Маленькая неуютная квартира",
	"Огромный прекрасный дворец",
	"Маленький ужасный дворец",
	"Красивый гостевой домик",
	"Некрасивый негостеприимный домик",
	"Уютное бунгало далеко от моря",
	"Неуютное бунгало по колено в воде"
],
shuffledOfferTitles = [...offerTitles].sort(() => Math.random() > 0.5),
types = ["flat", "house", "bungalo"],
checks = ["12:00", "13:00", "14:00"],
features = ["wifi", "dishwasher", "parking", "washer", "elevator", "conditioner"];

const result = [...Array(8).keys()].map((id) => ({
	author: {
		avatar: `img/avatars/user0${id + 1}.png`
    },
	offer: {
		title: shuffledOfferTitles[id],
		address: "location.x, location.y",
		price: random(1000, 1000000),
		type: types[random(0, types.length)],
		rooms: random(1, 5),
		guests: random(1, 9),
		checkin: checks[random(0, checks.length)],
		checkout: checks[random(0, checks.length)],
		features: ((rnd) => features.slice(random(0, rnd), random(rnd, features.length)))(random(0, features.length -1)),
		description: "",
		photos: []
    },
	location: {
		x: random(300, 900),
		y: random(100, 500)
    }
}));