设X[0:n-1]和Y[0:n-1]为两个数组，每个数组中含有n个已排好序的数。试设计一个O（logn）时间算法，找出X和Y的2n个数的中位数并输出。-Set X and Y [0: n- 1] [0: n- 1) for the two arrays, each array containing n number that have been sequenced. Try to design a O (logn) time algorithm, to find out in the median number of 2 n number of X and Y and output