空间O(1),时间O(n)
/**
* Created by king on 2017/5/6.
*
* 功能:随机输出10个字母,不重复
*/
public class TestRandom {
public static void main(String[] args) {
int ans=0; //int a[] = new int[26];
for(int i=0;i<10;)
{
int put = (int) (Math.random() * 26);
int n= 1 << put; //n相当于数组下角标
if ((ans&n)==0 ) {//if (a[put] == 0)
ans=ans|n; //a[put]=1;
i++;
System.out.println((char) (put + 65));
}
}
}
}