2022-02-02 2000. 反转单词前缀

java版本：

//stringbuffer可变字符串,substring截取字符串
class Solution {
    public String reversePrefix(String word, char ch) {
        int index=0;
        for(int i=0;i<word.length();i++){
            if(word.charAt(i)==ch){
           index=i;
           break;
            }
        }
        StringBuffer str=new StringBuffer(word.substring(0,index+1));
          str.reverse();
          str.append(word.substring(index+1));
          return str.toString();

    }
}