Problem

Implement an algorithm to determine if a string has all unique characters.
Input: "abcdefg"
Output: True
Input: "abcdefghijklmnopqrstuvwxyz"
Output: False

Solution

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = "abcdefghijklmnopqrstuvwxyz";
            Console.WriteLine(IsUnique(input));
            Console.ReadLine();
        }

        static bool IsUnique(string input)
        {
            //This solution is optimal because it uses a HashSet to store the characters.
            //The HashSet will not allow duplicates, so if the length of the HashSet is less than the length of the input string,
            //then there are duplicates.
            HashSet<char> set = new HashSet<char>();
            foreach (char c in input)
            {
                set.Add(c);
            }
            return set.Count == input.Length;
        }
    }
}