归并排序

def merge(a, b):
    c = []
    h = j = 0
    while j < len(a) and h < len(b):
        if a[j] < b[h]:
            c.append(a[j])
            j += 1
        else:
            c.append(b[h])
            h += 1

    if j == len(a):
        last = [i for i in b[h:] ]
    else:
        last = [i for i in a[j:] ]


    return c+last


def merge_sort(lists):
    if len(lists) <= 1:
        return lists
    middle = len(lists)//2
    left = merge_sort(lists[:middle])
    right = merge_sort(lists[middle:])
    return merge(left, right)

#测试用例
if __name__ == '__main__':
    a = [10, 1, 15, 32, 21]
    print (merge_sort(a))