LeetCode in Kotlin

324. Wiggle Sort II

Medium

Given an integer array nums, reorder it such that nums[0] < nums[1] > nums[2] < nums[3]....

You may assume the input array always has a valid answer.

Example 1:

Input: nums = [1,5,1,1,6,4]

Output: [1,6,1,5,1,4]

Explanation: [1,4,1,5,1,6] is also accepted.

Example 2:

Input: nums = [1,3,2,2,3,1]

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

Constraints:

• 1 <= nums.length <= 5 * 104
• 0 <= nums[i] <= 5000
• It is guaranteed that there will be an answer for the given input nums.

Follow Up: Can you do it in O(n) time and/or in-place with O(1) extra space?

Solution

class Solution {
    fun wiggleSort(nums: IntArray) {
        nums.sort()
        val result = IntArray(nums.size)
        var index = nums.size - 1
        var i = 1
        // Start filling all peaks (which is all at odd indexes) from start
        while (i < nums.size) {
            result[i] = nums[index]
            --index
            i += 2
        }
        // Start filling all valleys (which is all at even indexes) from end
        // why from end, as the last peak index may have smallest largest value, so to
        // make sure, that is also '>', fill in the smallest element near it.
        i = if ((nums.size - 1) % 2 == 0) nums.size - 1 else nums.size - 2
        index = 0
        while (i >= 0) {
            result[i] = nums[index]
            ++index
            i -= 2
        }
        System.arraycopy(result, 0, nums, 0, nums.size)
    }
}

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