Max Score from Cards(Swift: Sliding Window)

max_score_from_cards.swift

class Solution {
    func maxScore(_ arr: [Int], _ k: Int) -> Int {
        var windowSum = 0 
        for i in 0..<k {
            windowSum += arr[i]
        }
        
        var i = k - 1, j = arr.count - 1
        var bestSum = windowSum
        while i >= 0 {
            windowSum = windowSum + arr[j] - arr[i]
            bestSum = max(bestSum, windowSum)
            i -= 1
            j -= 1
        }
        return bestSum
    }
}