Problem
An integer n is strictly palindromic if, for every base b between 2 and n - 2 (inclusive), the string representation of the integer n in base b is palindromic.
Given an integer n, return true if n is strictly palindromic and false otherwise.
A string is palindromic if it reads the same forward and backward.
Testcases
Example 1
Input: n = 9
Output: false
Example 2
Input: n = 4
Output: false
Initial Result
Time spent: 10 min
Pass. I got a slower solution from calculating all possible string representation in other bases and returning False when I encountered a violation of the palindromic property.
Initial Approach
Calculate the strings for lower bases and then return False if no longer palindromic.
What I Missed
No values 4 or higher are strictly palindromic. This pattern isn’t hard to see if you consider the possibility. A base n-2 is always represented as 1 * x + 2 * y for integers x and y, violating the palindromic principle.
Approach to the Solution
Return False (since our problem is bounded to have inputs at minimum 4).
Key Takeaways
Review obscure (but not too obscure) binary properties.