經典的反轉

def reverseArr(arr, start, end):
    while(start < end):
        arr[start], arr[end] = arr[end], arr[start]
        start +=1;
        end -=1

def fun(arr,d, n):
    reverseArr(arr,0, n-1)
    reverseArr(arr, n-d, n-1)
    reverseArr(arr,0, n-d-1)

arr = [1,2,3,4,5,6,7]
fun(arr,2,len(arr))
print(arr)