2396. Strictly Palindromic Number

문제)

2396. Strictly Palindromic Number

 

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.

 

Example 1:

Input: n = 9
Output: false
Explanation: In base 2: 9 = 1001 (base 2), which is palindromic.
In base 3: 9 = 100 (base 3), which is not palindromic.
Therefore, 9 is not strictly palindromic so we return false.
Note that in bases 4, 5, 6, and 7, n = 9 is also not palindromic.

Example 2:

Input: n = 4
Output: false
Explanation: We only consider base 2: 4 = 100 (base 2), which is not palindromic.
Therefore, we return false.

 

Constraints:

• 4 <= n <= 105

 

솔루션1)

- 2부터 n-2까지 반복하면서 진수변환해서 palindrome를 체크

class Solution:
    def isStrictlyPalindromic(self, n: int) -> bool:        
        for i in range(2, n-1):
            val = self.convert_to_base_n(n, i)            
            if val != val[::-1]:
                return False
        return True
    
    def convert_to_base_n(self, num, n):
        ret = []
        while num:
            num, remainder = divmod(num, n)
            ret.append(str(remainder))        
        return ''.join(ret.reverse())