Suppose we have a value n. We have to find all upside down numbers of length n. As we knot the upside down number is one that appears the same when flipped 180 degrees.
So, if the input is like n = 2, then the output will be ['11', '69', '88', '96'].
To solve this, we will follow these steps −
Define a function middle() . This will take x
if x is 0, then
return list of a blank string
if x is same as 1, then
return a new list of elements 0, 1, 8
ret := a new list
mid := middle(x − 2)
for each m in mid, do
if x is not same as n, then
insert ("0" concatenate m concatenate "0") at the end of ret
insert ("1" concatenate m concatenate "1") at the end of ret
insert ("6" concatenate m concatenate "9") at the end of ret
insert ("8" concatenate m concatenate "8") at the end of ret
insert ("9" concatenate m concatenate "6") at the end of ret
return ret
From the main method, do the following −
if n is 0, then
return a new list
otherwise return sorted list of middle(n)
Let us see the following implementation to get better understanding −
Example
class Solution:
def solve(self, n):
if not n:
return []
def middle(x=n):
if not x:
return [""]
if x == 1:
return list("018")
ret = []
mid = middle(x - 2)
for m in mid:
if x != n:
ret.append("0" + m + "0")
ret.append("1" + m + "1")
ret.append("6" + m + "9")
ret.append("8" + m + "8")
ret.append("9" + m + "6")
return ret
return sorted(middle())
ob = Solution()
print(ob.solve(2))Input
2
Output
['11', '69', '88', '96']