determine if a string has all unique characters

要考虑的因素：构成字符串的字符集多大？ 是ASCII字符吗？还是26个字母，还是更大的字符集

public class UniqueChar
{
	public static void main(String[] args)
	{
		String s1="abcd124";
		String s2= "abacd234gaf";
		String s3="abcd";
		String s4="abcdeb";
		System.out.println("unique1: true?  ="+isUnique1(s1));
		System.out.println("unique11: true?  ="+isUnique11(s1));
		System.out.println("unique11: false?  ="+isUnique11(s2));
		System.out.println("unique1: false?  ="+isUnique1(s2));
		System.out.println("unique2: true?  ="+isUnique2(s3));
		System.out.println("unique2: false?  ="+isUnique2(s4));
		
	}
	//ASCII码集，如果是字母就把boolean改为26就OK
	public static boolean isUnique1(String s){
		boolean[] char_set =new boolean[256];
		for(int i=0; i0 会出现int 无法转为Boolean*/
			 if((check & (1 << index))>0) return false;
			 check |= (1 << index);
		}
		return true;
	}
	//那么ASCII码可以用8个int型来存放，可以用int[8]，我们通过指定字符除以32得到所在的元素下标，其余数是其位
	public static boolean isUnique11(String s){
		int[]  check =new int[8];
		for(int i=0;i0) return false;
			check[index] |= (1 << offset);	
		}
		return true;
	}
}