public String reverseVowels(String s) {
        if(s==null || s.isEmpty()) return s;
        StringBuilder sb=new StringBuilder(s);
        List<Integer> list=new ArrayList<>();
        for(int i=0;i<sb.length();++i){
            if("aeiouAEIOU".contains(""+sb.charAt(i))){
                list.add(i);
            }
        }
        Integer[]arr=list.toArray(new Integer[]{});
        int i=0,j=arr.length-1;
        while (i<j){
            char ch=sb.charAt(arr[i]);
            sb.setCharAt(arr[i],sb.charAt(arr[j]));
            sb.setCharAt(arr[j],ch);
            i++;
            j--;
        }
        return sb.toString();
    }