public class Test4 {
static char[] ch;
static int index=0;
static int b_num=0;
static int i_num=0;
static int n_num=0;
static int num=0;

public static void main(String[] args) {

System.out.println(getNum("iinbinbinginng"));
}

public static int getNum(String str){
ch=str.toCharArray();
for (int i = 0; i < ch.length; i++) {
switch (ch[i]) {
case 'b':
b_num++;
break;
case 'i':
i_num+=b_num;
break;
case 'n':
n_num+=i_num;
break;
case 'g':
num+=n_num;
break;
default:
break;
}
}
return num%(10^9+7);
}
}

这就是效率啊，思路清晰，借用别人的帖子。