LeetCode in Kotlin

3260. Find the Largest Palindrome Divisible by K

Hard

You are given two positive integers n and k.

An integer x is called k-palindromic if:

• x is a palindrome.
• x is divisible by k.

Return the largest integer having n digits (as a string) that is k-palindromic.

Note that the integer must not have leading zeros.

Example 1:

Input: n = 3, k = 5

Output: “595”

Explanation:

595 is the largest k-palindromic integer with 3 digits.

Example 2:

Input: n = 1, k = 4

Output: “8”

Explanation:

4 and 8 are the only k-palindromic integers with 1 digit.

Example 3:

Input: n = 5, k = 6

Output: “89898”

Constraints:

• 1 <= n <= 105
• 1 <= k <= 9

Solution

class Solution {
    fun largestPalindrome(n: Int, k: Int): String {
        val sc = CharArray(n)
        if (k == 1 || k == 3 || k == 9) {
            sc.fill('9')
        } else if (k == 7) {
            if (n == 1) {
                return "7"
            } else if (n == 2) {
                return "77"
            }
            val mod = n % 12
            checkValues(n, mod, sc)
        } else if (k == 2) {
            sc.fill('9')
            sc[0] = '8'
            sc[n - 1] = '8'
        } else if (k == 4) {
            sc.fill('8')
            var i = 2
            var j = n - 3
            while (i <= j) {
                sc[i] = '9'
                sc[j] = '9'
                ++i
                --j
            }
        } else if (k == 5) {
            sc.fill('9')
            sc[0] = '5'
            sc[n - 1] = '5'
        } else if (k == 6) {
            val number = getString(n, sc)
            if (number != null) {
                return number
            }
        } else if (k == 8) {
            sc.fill('8')
            var i = 3
            var j = n - 4
            while (i <= j) {
                sc[i] = '9'
                sc[j] = '9'
                ++i
                --j
            }
        }
        return String(sc)
    }

    private fun checkValues(n: Int, mod: Int, sc: CharArray) {
        if (mod == 6 || mod == 0) {
            sc.fill('9')
        } else if (mod == 3) {
            sc.fill('9')
            sc[n / 2] = '5'
        } else if (mod == 4 || mod == 5 || mod == 1 || mod == 2) {
            sc.fill('7')
            var i = 0
            var j = n - 1
            while (i + 1 < j) {
                sc[i] = '9'
                sc[j] = '9'
                ++i
                --j
            }
        } else if (mod == 7 || mod == 8 || mod == 10 || mod == 11) {
            sc.fill('4')
            var i = 0
            var j = n - 1
            while (i + 1 < j) {
                sc[i] = '9'
                sc[j] = '9'
                ++i
                --j
            }
        } else if (mod == 9) {
            sc.fill('9')
            sc[n / 2] = '6'
        }
    }

    private fun getString(n: Int, sc: CharArray): String? {
        if (n == 1) {
            return "6"
        } else if (n == 2) {
            return "66"
        } else {
            if (n % 2 == 1) {
                sc.fill('9')
                sc[0] = '8'
                sc[n - 1] = '8'
                sc[n / 2] = '8'
            } else {
                sc.fill('9')
                sc[0] = '8'
                sc[n - 1] = '8'
                sc[n / 2] = '7'
                sc[n / 2 - 1] = '7'
            }
        }
        return null
    }
}

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