LeetCode in Kotlin

932. Beautiful Array

Medium

An array nums of length n is beautiful if:

• nums is a permutation of the integers in the range [1, n].
• For every 0 <= i < j < n, there is no index k with i < k < j where 2 * nums[k] == nums[i] + nums[j].

Given the integer n, return any beautiful array nums of length n. There will be at least one valid answer for the given n.

Example 1:

Input: n = 4

Output: [2,1,4,3]

Example 2:

Input: n = 5

Output: [3,1,2,5,4]

Constraints:

• 1 <= n <= 1000

Solution

class Solution {
    private var memo: MutableMap<Int, IntArray>? = null
    fun beautifulArray(n: Int): IntArray? {
        memo = HashMap()
        return helper(n)
    }

    private fun helper(n: Int): IntArray? {
        if (n == 1) {
            memo!![1] = intArrayOf(1)
            return intArrayOf(1)
        }
        if (memo!!.containsKey(n)) {
            return memo!![n]
        }
        val mid = (n + 1) / 2
        val left = helper(mid)
        val right = helper(n - mid)
        val rst = IntArray(n)
        for (i in 0 until mid) {
            rst[i] = left!![i] * 2 - 1
        }
        for (i in mid until n) {
            rst[i] = right!![i - mid] * 2
        }
        memo!![n] = rst
        return rst
    }
}

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