insertion sort

insertion sort用来sort基本sort好的序列，时间是O(n)

def insertionSort(alist):

   for index in range(1, len(alist)):
     currentvalue = alist[index]
     position = index
     while position>0 and alist[position-1]>currentvalue:
         alist[position]=alist[position-1]
         position = position-1

     alist[position]=currentvalue

alist = [54,26,93,17,77,31,44,55,20]
insertionSort(alist)
print(alist)