Detecting if a string has unique characters: comparing my solution to “Cracking the Coding Interview?”

Question

I am working through the book \"Cracking the Coding Interview\" and I have come across questions here asking for answers, but I need help comparing my answer to the solution

Answer 1

This is the necessary correction to the book's code:

public static boolean checkForUnique(String str){
    boolean containsUnique = false;

    for(char c : str.toCharArray()){
        if(str.indexOf(c) == str.lastIndexOf(c)){
            containsUnique = true;
        } else {
            return false;
        }
    }

    return containsUnique;
}