Only unique chars into string?, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var str = "This is not supposed to be a unique string.";
            //var str = "String";
            
            // Method 1
            var checkedChars = new List<char>();
            var result = true;
            foreach(char c in str){
                if(!checkedChars.Contains(c))
                   checkedChars.Add(c);
                else{
                   result = false;
                   break;
                }
            }

// Method 1
            var result2 = str.Distinct().Count() == str.Length;

// Throw results.
            Console.WriteLine("Is unique the list of chars in string? {0}, {1}", result, result2);
        }
    }
}

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Compilation time: 0,16 sec, absolute running time: 0,09 sec, cpu time: 0,06 sec, average memory usage: 13 Mb, average nr of threads: 3