#792 · #1423 · Maximum Points You Can Obtain from Cards(可获得的最大点数)

There are several cards in a row with cardPoints[i] points. In each step you take one card from either the beginning or the end. You must take exactly k cards. Return the maximum score. Constraints: 1 <= k <= cardPoints.length <= 10^5, 1 <= cardPoints[i] <= 10^4.