determine if a string has all unique characters?

Question

Can anybody tell me how to implement a program to check a string contains all unique chars ?

Answer 1

this is optimal solution for the problem. it takes only an integer variable and can tell whether it is unique or not regardless of string size.

complexity

best case O(1)

worst case O(n)

public static boolean isUniqueChars(String str) {
    int checker = 0;
    for (int i = 0; i < str.length(); ++i) {
        int val = str.charAt(i) - ‘a’;
        if ((checker & (1 << val)) > 0) 
            return false;
        checker |= (1 << val);
    }
    return true;
}