WiggleSort.swift

/**
 * Question Link: https://leetcode.com/problems/wiggle-sort/
 * Primary idea: Iterate the array and swap the largest one to the middle
 * Time Complexity: O(n), Space Complexity: O(1)
 */

class WiggleSort {
    func wiggleSort(_ nums: inout [Int]) {
        guard nums.count >= 2 else {
            return
        }
        
        for i in stride(from: 1, to: nums.count, by: 2) {
            let idx = getLargest(nums, i - 1, i , i + 1)
            (nums[i], nums[idx]) = (nums[idx], nums[i])
        }
    }
    
    private func getLargest(_ nums: [Int], _ x: Int, _ y: Int, _ z: Int) -> Int {
        let len = nums.count
    
        let xVal = x >= 0 && x < len ? nums[x] : Int.min
        let yVal = y >= 0 && y < len ? nums[y] : Int.min
        let zVal = z >= 0 && z < len ? nums[z] : Int.min
        let maxVal = max(xVal, yVal, zVal)
        
        if maxVal == xVal {
            return x
        } else if maxVal == yVal {
            return y
        } else {
            return z
        }
    }
}