How to find the duplicates from Datatable and store them to the excel

Am retrieving data and building the data table ,now how can i find out the duplicates in the datatable and store it to the excel.
for example orginal name :masterdata and duplicate name: masterdata-ALT (this duplicate name is always suffixed with orginal name as mentioned in the example above)

can please somebody help me with this?

@Spoorthi_Chintala1 - you can try below

masterdata-ALT= (from d in masterdata.Select() where( From m in masterdata.Select() where string.Join(",",m.ItemArray).Equals(string.Join(",",d.ItemArray)) Select m).ToArray.Count>1 Select d).ToArray.CopyToDataTable()

you can write the duplicate datatable to excel…