Problem

There are several cards arranged in a row, and each card has an associated number of points The points are given in the integer array cardPoints.

In one step, you can take one card from the beginning or from the end of the row. You have to take exactly k cards.

Your score is the sum of the points of the cards you have taken.

Given the integer array cardPoints and the integer k, return the maximum score you can obtain.

Constraints:

• 1 <= cardPoints.length <= 10^5
• 1 <= cardPoints[i] <= 10^4
• 1 <= k <= cardPoints.length

Example1

Input: cardPoints = [1,2,3,4,5,6,1], k = 3
Output: 12
Explanation: After the first step, your score will always be 1. However, choosing the rightmost card first will maximize your total score. The optimal strategy is to take the three cards on the right, giving a final score of 1 + 6 + 5 = 12.

Example2

Input: cardPoints = [2,2,2], k = 2
Output: 4
Explanation: Regardless of which two cards you take, your score will always be 4.

Example3

Input: cardPoints = [9,7,7,9,7,7,9], k = 7
Output: 55
Explanation: You have to take all the cards. Your score is the sum of points of all cards.

Example4

Input: cardPoints = [1,1000,1], k = 1
Output: 1
Explanation: You cannot take the card in the middle. Your best score is 1.

Example5

Input: cardPoints = [1,79,80,1,1,1,200,1], k = 3
Output: 202

Solution

class Solution {
public:
    int maxScore(vector<int>& cardPoints, int k) {
        int wnd_sz = cardPoints.size() - k;

        int total_score = 0;
        for(int i = 0;i<cardPoints.size();++i)
            total_score += cardPoints[i];
        
        int wnd_score = 0;
        int ret = 0;
        for(int i = 0,j = 0;i<cardPoints.size();++i)
        {
            wnd_score += cardPoints[i];
            while(i - j + 1 > wnd_sz)
            {
                wnd_score -= cardPoints[j];
                ++j;
            }

            if(i-j +1 == wnd_sz)
                ret = max(ret,total_score - wnd_score);

        }

        return ret;

    }
};