丑陋的字符串2

import java.util.Scanner;
public class 丑陋的字符串 {
public static void main(String[] args) {

    Scanner sr = new Scanner(System.in);    String s = sr.next();    StringBuilder sb = new StringBuilder(s);    int index = 0;    while(index<sb.length() && sb.charAt(index)=='?'){        index++;    }    for(int i=index+1;i<sb.length();i++){        if(sb.charAt(i)=='?'){            if(sb.charAt(i-1)=='A')                sb.replace(i, i+1, "B");            else                sb.replace(i, i+1, "A");        }    }    System.out.println(count(sb.toString(),index));}private static int count(String str, int index) {    int count = 0;    for(int i=index+1;i<str.length();i++){        if(str.charAt(i) == str.charAt(i-1))            count++;    }    return count;}

}