BearAndSteadyGene.java

// https://www.hackerrank.com/challenges/bear-and-steady-gene/problem

package strings;

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class BearAndSteadyGene {
    private static int n;

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        n = scanner.nextInt();
        String s = scanner.next();
        Map<Character, Integer> map = new HashMap<>();
        map.put('A', 0);
        map.put('C', 0);
        map.put('G', 0);
        map.put('T', 0);
        for (Character c : s.toCharArray())
            map.put(c, map.get(c) + 1);

        int left = 0, right = 0, min = Integer.MAX_VALUE;
        while(right < n - 1){
            char rc = s.charAt(right++);
            map.put(rc, map.get(rc) - 1);
            while(isSteady(map)){
                min = Math.min(min, right - left);
                char lc = s.charAt(left++);
                map.put(lc, map.get(lc) + 1);
            }
        }
        System.out.println(min);
    }

    private static boolean isSteady(Map<Character, Integer> map) {
        for (Integer i : map.values())
            if (i > n / 4) return false;
        return true;
    }
}