java判断字符是否唯一

输入: s = "leetcode"
输出: false 

输入: s = "abc"
输出: true

class Solution {
    public boolean isUnique(String astr) {
    for (char ch: astr.toCharArray()){
        if (astr.indexOf(ch) != astr.lastIndexOf(ch)) {
        	return false;
        }
    }
    return true;
}
}

 public boolean isUnique(String astr) {
        long low64 = 0;
        long high64 = 0;
        for (char c : astr.toCharArray()) {
            if (c >= 64) {
                long bitIndex = 1L << c - 64;
                if ((high64 & bitIndex) != 0) {
                    return false;
                }
                high64 |= bitIndex;
            } else {
                long bitIndex = 1L << c;
                if ((low64 & bitIndex) != 0) {
                    return false;
                }
                low64 |= bitIndex;
            }
        }
        return true;
    }