Check Duplicates in a ArrayList

ArrayList list = new ArrayList { 1, 9, 2, 1, 6, 5 };

Above is a array list of integers. We can use below methods to check the duplicates in the array list.

Method 1: Using the Contains method

private void AddItems(object o) 

 { 

  if(!list.Contains(o))
   { 

    list.Add(o); 

   }
 else
  {
   //Duplicate found
  } 

}

Method 2: Using LINQ

var x = from l in list.OfType() 

 group l by l into g 

 where g.Count() > 1 

 select g.Key; 

 if (x.Count() > 0) 

 { 

   // Duplicate found 

 }