Longest substring without repeat #95

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        string s = "toolliyo";
        var seen = new Dictionary<char, int>();
        int best = 0, start = 0;
        for (int j = 0; j < s.Length; j++) {
            if (seen.ContainsKey(s[j]) && seen[s[j]] >= start) start = seen[s[j]] + 1;
            seen[s[j]] = j;
            best = Math.Max(best, j - start + 1);
        }
        Console.WriteLine(best);
    }
}