说明：  合并排序算法是用分治策略实现对n个元素进行排序的算法。其基本思想是：将待排序的元素分成大小大致相同的2个子集合，分别对2个子集合进行排序，最终将排好序的子集合合并成为所要求的排好序的集合。算法复杂度为：O(nlogn)
(Merge sorting algorithm is used to realize sub-rule strategy to sort n elements of the algorithm. The basic idea is: the element will be sorted into roughly the same size of the 2 sub-assembly, respectively, to 2 sub-collection sort sequence will eventually lined the subset required by the merger of scheduling a collection of good order. Algorithm complexity is: O (nlogn))