2384. Largest Palindromic Number
Medium
You are given a string num consisting of digits only.
Return the largest palindromic integer (in the form of a string) that can be formed using digits taken from num. It should not contain leading zeroes.
Notes:
- You do not need to use all the digits of
num, but you must use at least one digit. - The digits can be reordered.
Example 1:
Input: num = "444947137" Output: "7449447" Explanation: Use the digits "4449477" from "444947137" to form the palindromic integer "7449447". It can be shown that "7449447" is the largest palindromic integer that can be formed.
Example 2:
Input: num = "00009" Output: "9" Explanation: It can be shown that "9" is the largest palindromic integer that can be formed. Note that the integer returned should not contain leading zeroes.
Constraints:
1 <= num.length <= 105numconsists of digits.
class Solution:
def largestPalindromic(self, num: str) -> str:
# counting the number of occurrence of each digit
count = Counter(num)
# if the occurrence is multiple of 2, we'll take then in descending order and remove if there any leading zero (0)
res = "".join(count[i] // 2 * i for i in '9876543210').lstrip("0")
# taking the max of the odd number(s) of occurrence of digit
mid = max(count[i]%2 * i for i in count)
return (res+mid+res[::-1]) or "0"