Bear And Steady Gene - binary search algorithm

BearAndSteadyGene_Binarysearch.cs

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

namespace BearAndSteadyGene_BinarySearch
{
    /*
     *  March 6, 2016
     *  code source:
     *  java code: https://gist.github.com/jianminchen/d01faa03ca9b06696db3
     *  convert it to C# code 
     */
    class BearAndSteadyGene_BinarySearch
    {
        static  String GENES = "ACGT";

        static void Main(string[] args)
        {
            int N = Int32.Parse(Console.ReadLine());

            string line = Console.ReadLine();

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

        public static int solve(int n, string s) {
		
		    int[] a = new int[n];
		
		    int need = n / 4;
		
		    int[] cnt = new int[4];
		    for (int i = 0; i < n; i++) {
			    a[i] = indexOfGENES(s[i]);
			    cnt[a[i]]++;
		    }
		
		    if (cnt[0] == need && cnt[1] == need && cnt[2] == need && cnt[3] == need) {			
			    return 0;
		    }
		
		    int low = 0;
		    int high = n;
		
		    while (high - low > 1) { // >1, confused here as well. 
			    int mid = (low + high) >> 1;
			
			    int[] tmp = cloneF(cnt);
			    for (int i = 0; i < mid; i++) {
				    tmp[a[i]]--;
			    }
			
			    if (tmp[0] <= need && tmp[1] <= need && tmp[2] <= need && tmp[3] <= need) {
				    high = mid;
				    continue ;
			    }

                bool isBreak = false;
			    for (int i = mid; i < n; i++) {
				    tmp[a[i - mid]]++;  // test case: GAAATAAA, cannot figure out why we need to add tmp[a[0]]
				    tmp[a[i]]--;
				
				    if (tmp[0] <= need && tmp[1] <= need && tmp[2] <= need && tmp[3] <= need) {
					    high = mid;
                        isBreak = true;
                        break; // two loops, only break nearest loop for 
				    }
			    }
			
                if(!isBreak)
			        low = mid;
		    }
		
		    return high;		
	}

    private static int indexOfGENES(char c)
    {
        for (int i = 0; i < GENES.Length; i++)
            if (c == GENES[i])
                return i;

        return -1; 
    }     

    private static int[] cloneF(int[] cnt)
    {
        int[] ret = new int[4]; 

        for(int i=0; i<4; i++)
            ret[i] = cnt[i]; 

        return ret; 
    }
    }
}