LeetCode in Kotlin

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 <= 105
• num consists of digits.

Solution

class Solution {
    fun largestPalindromic(num: String): String {
        val count = IntArray(10)
        var center = -1
        val first = StringBuilder()
        for (c in num.toCharArray()) {
            count[c.code - '0'.code]++
        }
        var c: Int
        for (i in 9 downTo 0) {
            c = 0
            if (count[i] % 2 == 1 && center == -1) {
                center = i
            }
            if (first.length == 0 && i == 0) {
                continue
            }
            while (c < count[i] / 2) {
                first.append(i.toString())
                c++
            }
        }
        val second: StringBuilder = StringBuilder(first.toString())
        if (center != -1) {
            first.append(center)
        }
        first.append(second.reverse().toString())
        return if (first.length == 0) "0" else first.toString()
    }
}

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