Highlight duplicate rows in GridView in ASP.Net

This way

HTML

<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
    runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField DataField="Id" HeaderText="Id" ItemStyle-Width="30" />
        <asp:BoundField DataField="Name" HeaderText="Name" ItemStyle-Width="150" />
        <asp:BoundField DataField="Country" HeaderText="Country" ItemStyle-Width="150" />
    </Columns>
</asp:GridView>

Namespaces

using System.Data;
using System.Drawing;

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id", typeof(int)),
                        new DataColumn("Name", typeof(string)),
                        new DataColumn("Country",typeof(string)) });
        dt.Rows.Add(1, "John Hammond", "United States");
        dt.Rows.Add(2, "Mudassar Khan", "India");
        dt.Rows.Add(3, "Suzanne Mathews", "France");
        dt.Rows.Add(4, "Robert Schidner", "Russia");
        dt.Rows.Add(4, "Robert Schidner", "Russia");
        GridView1.DataSource = dt;
        GridView1.DataBind();
        HighlightDuplicate(this.GridView1);
    }
}

public void HighlightDuplicate(GridView grv)
{
    //use the currentRow to compare against
    for (int currentRow = 0; currentRow < grv.Rows.Count - 1; currentRow++)
    {
        GridViewRow rowToCompare = grv.Rows[currentRow];
        //specify otherRow as currentRow + 1
        for (int otherRow = currentRow + 1; otherRow < grv.Rows.Count; otherRow++)
        {
            GridViewRow row = grv.Rows[otherRow];

            bool duplicateRow = true;
            //compare cell ENVA_APP_ID between the two rows
            if (rowToCompare.Cells[0].Text != row.Cells[0].Text)
            {
                duplicateRow = false;
                break;
            }
            //highlight both the currentRow and otherRow if ENVA_APP_ID matches 
            if (duplicateRow)
            {
                rowToCompare.BackColor = Color.Red;
                rowToCompare.ForeColor = Color.Black;
                row.BackColor = Color.Red;
                row.ForeColor = Color.Black;
            }
        }
    }
}

Screenshot