arr=[7,4,2,13,6,5,3,6,17,1]
for i in range(1,len(arr)):
key=arr[i]
j=i
while :
arr[j]=arr[j-1]
j-=1
①j>0 and key<arr[j-1] ②j>=0 and key<arr[j-1] ③arr[j]=key ④arr[j-1]=key