Two string - using dictionary(int, char) - int - just a number starting from zero

TwoString14.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
class Solution {
    static void Main(String[] args)
        {
            /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution */
            int n_tc = Convert.ToInt32(Console.ReadLine());
            for (int i = 0; i < n_tc; i++)
            {
                var string1 = Console.ReadLine();
                var string2 = Console.ReadLine();
                Console.WriteLine(ValidateString(string1, string2) == false ? "NO" : "YES");
            }
        }

        static bool ValidateString(string str1, string str2)
        {
            Dictionary<int,char> dex = new Dictionary<int,char>();
            int count = 0;
            foreach (char i in str1)
            {
                if (!dex.ContainsValue(i))
                    dex.Add(count, i);
                count++;
            }
            var returnValue = false;
            foreach (char i in str2)
            {
                returnValue = dex.ContainsValue(i);
                if (returnValue)
                    return returnValue;
            }
            return returnValue ;
        }
}