具体地讲，如果一个数组A[1..n]中超过半数的元素都相同时，该数组被称为含有一个主元素。

(a) 设计一个有效算法（至少是O(n logn)），确定该数组中是否含有一个主元素，如果有，找出这个元素。 (为简单起见，假设n是2的幂，且n<150)

(b) 能否给出一个线性时间算法？

需注意的是，该数组的元素之间可能不存在顺序——即不能进行”A[i]<A[j]”的判断，但是可以进行是否相等的判断。

-Specifically, if an array A [1 .. n] more than half of the elements are the same, the array is known as a main element contains. (A) to design an effective algorithm (at least O (n logn)), to determine whether the array contains a primary element, and if so, find out the elements. (For simplicity, assume that n is a power of 2, and n < 150) (b) can give a linear time algorithm? It must be noted that the array may not exist between the elements of the order- that can not be " A [i] <A[j]”的判断，但是可以进行是否相等的判断。