Bear and Steady Gene - add comment to explain the for loop - sliding window design

BearAndSteadyGene_4th_AddComment.cs

using System;
using System.Collections.Generic;
using System.IO;

class Solution
{
    /*
     * Julia write the C# code, 
     * code source: Java code
     * https://gist.github.com/jianminchen/d52ced38de0bffa2d9e8
     */
    static void Main(String[] args)
    {
        int N = Int32.Parse(Console.ReadLine());

        string line = Console.ReadLine();

        Console.WriteLine(getMinimumSubstring(N, line));
    }

    public static int getMinimumSubstring(int n, string s)
    {
        int mx = n / 4;

		int[] cnt = new int[256];

		foreach (char c in s) {
			cnt[c]++;
		}

		string t = "ACGT";
		bool ok = true;
		foreach (char c in t) {
			if (cnt[c] > mx) {
				ok = false;
			}
		}

		if (ok) 			
			return 0;		
        /*
		int r = 0;

		int ans = n;
		for (int l= 0; l < n; l++) {
			while (cnt['A'] > mx || cnt['C'] > mx || cnt['T'] > mx || cnt['G'] > mx) {
				if (r == n) {					
					return ans;
				}

				--cnt[s[r]];
				++r;
			}
			ans = Math.Min(ans, r - l);
			++cnt[s[l]];
		}

        return ans; 
         * */
        return getMinimumLength(cnt, n, mx, s); 
    }   

    /*
     * sliding window: 
     * start pointer: l
     * end pointer:   r
     * 
     * For example: 
     * GAAATAAA
     * 
     * windows l=0, r=0, size of window is 0; 
     * 
     * First, loop on start pointer l, 
     * when l = 0, keep the start pointer as is, move end pointer until the rest of string
     * satisfies condition: any char in "ACGT"'s count <= mx, for test case GAAATAAA, mx =2 
     * 
     * r = 6, exit while loop inside for loop
     * sliding windows is l=0, r=6. 
     * In other words, string "GAAATA" is one of strings. 
     * 
     * Then, sliding window's start pointer l increases to next value 1, and then, repeat the process. 
     * "AAATA" is also one of strings, but length is shorter than "GAAATA". 
     */
    private static int getMinimumLength(int[] cnt, int n, int mx, string s)
    {
        int r = 0; 
        int ans = n;
        for (int l = 0; l < n; l++) // 
        {
            while (cnt['A'] > mx || cnt['C'] > mx || cnt['T'] > mx || cnt['G'] > mx)
            {
                if (r == n)
                {
                    return ans;
                }

                --cnt[s[r]];
                ++r;
            }
            ans = Math.Min(ans, r - l);
            ++cnt[s[l]];
        }

        return ans; 
    }
}