प्रस्तावित अक्षरों C# के आधार पर शब्दकोश से सबसे लंबा शब्द ढूंढें

Hello everyone, please and need your help.
I have three text boxes on the windows form:
- In tetxBox1.Text there is a dictionary with many words (the longest words 
  have 12 letters)
- There are always 12 letters offered in textBox2.Text
- In textBox3.Text, I want the result to be longest word from textBox1 
  composed of offered words from textBox2

For example:

In textBox1.Text I have the following words:

characters
character
charity
act
acter
acted
successfully
wind
succession
windy
successful
window
windows
success
excellent
excel
excellence
excellency

In textBox2.Text I have following 12 letters offered:

euclsfcysuls

In textBox3.Text I want as result longest word from textBox1.Text than words from textBox2.Text:

successfully


I am asking for your help if it is possible, some solution...
I hope you understood me, I apologize for my English if you didn't understand.
Thank you all in advance.

https://i.postimg.cc/HnS59c2R/Capture.png[^]

मैंने क्या प्रयास किया है:

static bool isSubSequence(String str1,
                                String str2)
        {
            int m = str1.Length, n = str2.Length;

            int j = 0; 

            for (int i = 0; i < n && j < m; i++)
            {
                if (str1[j] == str2[i])
                {
                    j++;
                }
            }
            return (j == m);
        }


static String findLongestString(List<String> dict,
                                            String str)
        {
            String result = "";
            int length = 0;
            foreach (String word in dict)
            {
                if (length < word.Length &&
                    isSubSequence(word, str))
                {
                    result = word;
                    length = word.Length;
                }
            }

            return result;
        }

private void btnfind_Click(object sender, EventArgs e)
        {
            String[] arr = textBox1.Lines;
            List<String> dict = new List<String>(arr);
            String str = textBox2.Text;
            textBox3.Text = (findLongestString(dict, str));
        }