Taking k cards from the ends is equivalent to leaving a contiguous subarray of size n - k in the middle! To maximize the sum of k cards, we must minimize the sum of the n - k cards left in the middle.

1. n = len(cardPoints), window_size = n - k.
2. If k == n, return sum(cardPoints).
3. Total sum of all cards.
4. Use sliding window to find the minimum sum of any subarray of size window_size.
5. Return total_sum - min_subarray_sum.

• Time Complexity: O(N).
• Space Complexity: O(1).

def max_score(cardPoints, k):
    n = len(cardPoints)
    window_size = n - k
    
    curr = sum(cardPoints[:window_size])
    min_sum = curr
    total = sum(cardPoints)
    
    for i in range(window_size, n):
        curr += cardPoints[i] - cardPoints[i - window_size]
        min_sum = min(min_sum, curr)
        
    return total - min_sum