Strobogrammatic number

Time: O(N); Space: O(1); easy

A mirror number is a number that looks the same when rotated 180 degrees (looked at upside down).

For example, the numbers “69”, “88”, and “818” are all mirror numbers.

Write a function to determine if a number is mirror. The number is represented as a string.

Have you met this question in a real interview?

Example 1:

Input: num = “69”

Output: True

Example 2:

Input: num = “68”

Output: False

[3]:

class Solution1(object):
    """
    Time: O(N)
    Space: O(1)
    """
    lookup = {'0':'0', '1':'1', '6':'9', '8':'8', '9':'6'}
    def isStrobogrammatic(self, num):
        """
        :type num: str
        :rtype: bool
        """
        n = len(num)
        for i in range((n+1) // 2):
            if num[n-1-i] not in self.lookup or \
               num[i] != self.lookup[num[n-1-i]]:
                return False
        return True

[4]:

s = Solution1()
num = "69"
assert s.isStrobogrammatic(num) == True
num = "68"
assert s.isStrobogrammatic(num) == False