[编程题] DNA片段分析代码

import java.util.*;

public class Main {

    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        
        String s = in.nextLine();
        
        in.close();
        
        System.out.println(helper(s));
    }
    
    
    private static int helper(String s) {
        
        String source = "ATGC";
        
        int res = 0;
        
        for(int i=0;i<s.length();i++) {
            
            
            if(source.indexOf(s.charAt(i) + "") != -1) {
                int index = i;
                index++;
                while(index < s.length() && source.indexOf(s.charAt(index) + "") != -1) {
                    index++;
                }
                if((index - i) > res)
                    res = index-i;
            }
            
            
        }
        
        return res;
        
    }
}