判断字符串中是否所有字符唯一

Question Implement an algorithm to determine if a string has all unique characters What if you can not use additional data structures ?

1.Assume the char set is ASCII(if not we need to increase the storage size):

public static boolean isUnique(String str){
    boolean[] char_set=new boolean[256];
    for(int i=0;i<str.length();i++{
        int val=str.charAt(i);
        if(char_set[val])return false;
        char_set[val]=true;
    }
    return true;
}

The time complexity is O(n) and space complexity is O(n). 2.Or you can use a bit vector to reduce the space usage.Assuming that the string is only lower case ‘a’ through ‘z’.

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;
}