Retain CheckBoxList selection on Form Submit in ASP.Net MVC

hello,

i have this comma seperated string a = 125, 253, 125  on page load i want to loop that if a value has in checkbox list so it should be checked on checbox list binding

i have this checkbox list binding,

@model List<MVCApp.Models.FirstCategories>
@using (@Html.BeginForm("CheckboxListTopcategoryMenu_post", "Application", FormMethod.Get))
{
    <input type="hidden" id="checkedCheckBoxes" name="checkedHobbies" />
    for (int i = 0; i < Model.Count(); i++)
    {
        @Html.HiddenFor(m => m[i].id)
        @Html.HiddenFor(m => m[i].Title)
        @Html.CheckBoxFor(m => m[i].isSelected)
        @Html.DisplayFor(m => m[i].Title)
    }
<input id="Button2" type="submit" class="btn red" value="Search" />
}

 method to checkboxlist binding

        public ActionResult CheckboxListTopcategoryMenu()
        {
            //Call first category in top category menu partial layout
            //DataTable ds = new DataTable();

            CategoriesBL fc = new CategoriesBL();

            //ds = fc.SelectFirstCategoriesBL();

            //Fille properties of contractIdetails

            return PartialView("CheckboxListTopcategoryMenu", fc.GetCategoriesBL());
        }

     public ActionResult CheckboxListTopcategoryMenu_post(List<FirstCategories> categoryselected)
     {
         string _searches = "";
         foreach (FirstCategories cat in categoryselected)
         { 
             if (cat.isSelected)
             {
                 _searches += cat.id.ToString() + ",";
             }
         } 
 
         string url = string.Format("/ads/search?search={0}", _searches);
         return Redirect(url);
         //return View();
     }