面试题 01.01. 判定字符是否唯一

Bit

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class Solution {
    public boolean isUnique(String astr) {
        if (astr.length() > 26) {
            return false;
        }
        
        int mask = 0;
        for (int i = 0; i < astr.length(); i++) {
            int offset = astr.charAt(i) - 'a';
            if ((mask & (1 << offset)) != 0) {
                return false;
            }
            
            mask |= (1 << offset);
        }

        return true;
    }
}

Sort

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class Solution {
    public boolean isUnique(String astr) {
        if (astr.length() > 26) {
            return false;
        }
        
        char[] chars = astr.toCharArray();
        Arrays.sort(chars);
        for (int i = 1; i < chars.length; i++) {
            if (chars[i] == chars[i - 1]) {
                return false;
            }
        }

        return true;
    }
}

References

面试题 01.01. 判定字符是否唯一