LeetCode in Kotlin
2217. Find Palindrome With Fixed Length
Medium
Given an integer array queries and a positive integer intLength, return an array answer where answer[i] is either the queries[i]th smallest positive palindrome of length intLength or -1 if no such palindrome exists.
A palindrome is a number that reads the same backwards and forwards. Palindromes cannot have leading zeros.
Example 1:
Input: queries = [1,2,3,4,5,90], intLength = 3
Output: [101,111,121,131,141,999]
Explanation:
The first few palindromes of length 3 are:
101, 111, 121, 131, 141, 151, 161, 171, 181, 191, 202, …
The 90th palindrome of length 3 is 999.
Example 2:
Input: queries = [2,4,6], intLength = 4
Output: [1111,1331,1551]
Explanation:
The first six palindromes of length 4 are:
1001, 1111, 1221, 1331, 1441, and 1551.
Constraints:
1 <= queries.length <= 5 * 1041 <= queries[i] <= 1091 <= intLength <= 15
Solution
class Solution {
fun kthPalindrome(queries: IntArray, intLength: Int): LongArray {
val minHalf = Math.pow(10.0, ((intLength - 1) / 2).toDouble()).toLong()
val maxIndex = Math.pow(10.0, ((intLength + 1) / 2).toDouble()).toLong() - minHalf
val isOdd = intLength % 2 == 1
val res = LongArray(queries.size)
for (i in res.indices) {
res[i] = if (queries[i] > maxIndex) -1 else helper(queries[i].toLong(), minHalf, isOdd)
}
return res
}
private fun helper(index: Long, minHalf: Long, isOdd: Boolean): Long {
var half = minHalf + index - 1
var res = half
if (isOdd) {
res /= 10
}
while (half != 0L) {
res = res * 10 + half % 10
half /= 10
}
return res
}
}