Bear and Steady Gene - study code - HackerRank - Nov. 28, 2016 - the code is very simple, try to figure out the idea.

BearAndSteadyGene_StudyCode1.cs

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

namespace BearAndSteadyGene2
{
    class BearAndSteadyGene2
    {               
        /*
         * Nov. 28, 2016
         * 
         */
        static void Main(string[] args)
        {
            int number = practice(8, "GAAATAAA"); 
        }

        /*
         * Nov. 28, 2016
         * 
         */
        private static int practice(int n, string input)
        {                      
            int[] a = new int[1007];             
            
            for (int i = 0; i < n; i++)
            {
                a[input[i]]++; 
            }

            int ans = Int32.MaxValue;
            int index = 0;
            for (int i = 0; i < n; i++)
            {
                a[input[i]]--;
                while (valid(n, a) && index <= i)
                {
                    ans = Math.Min(ans, i - index + 1);
                    a[input[index]]++;
                    index++; 
                }
            }

            return ans; 
        }

        private static bool valid(int n, int[] a)
        {
            int A, G, T, C;
            A = a['A'];
            G = a['G'];
            T = a['T'];
            C = a['C'];
            if (A <= n / 4 && G <= n / 4 && T <= n / 4 && C <= n / 4) return true;
            return false;
        }
    }
}