ASP.Net: Find smallest integer whose sum of digits is N

Hi dilhararangan,

Please refer below Sample.

 HTML

<asp:TextBox runat="server" ID="txtNumber" />
<asp:Button ID="Button1" Text="Next" runat="server" OnClick="Calculate" />
<hr />
<asp:Label ID="lblMessage" runat="server" />

Code

C#

protected void Calculate(object sender, EventArgs e)
{
    lblMessage.Text = Next(Convert.ToInt32(txtNumber.Text)).ToString();
}

private int Next(int n)
{
    int newNumber = -1;
    List<char> startChars = new List<char>();
    n.ToString().ToList().ForEach(x => startChars.Add(x));
    List<char> newChars = new List<char>();
    List<char> commonChars = null;
    while (commonChars == null || commonChars.Any())
    {
        if (n < Math.Pow(2, 31) || n > 0)
        {
            newNumber = n + 1;
            newChars.Clear();
            newNumber.ToString().ToList().ForEach(x => newChars.Add(x));
            commonChars = startChars.Intersect(newChars).ToList();
            n++;
        }
    }

    return newNumber;
}

Screenshot