class Solution {
    public boolean isUnique(String astr) {
        boolean flag = true;
        int count = astr.length();
        if (count != 0 || count != 1){
            for (int i = 0; i < count; i++){
                if (astr.indexOf(astr.charAt(i)) != astr.lastIndexOf(astr.charAt(i))){      // 利用索引判断从左从右索引值是否相同
                    flag = false;
                }
            }
        }
        return flag;
    }
}