從起點開始k個數的sum記為sum1，從終點開始k個數的sum記為sum2

如果sum1 > sum2，則說明相應長度取左邊價值會更大，取完之後sum1 - 當前“起點”，sum2 - 當前“終點”

否則，取右邊，sum1 - 當前“終點”，sum2 - 當前“起點”

相等時無所謂

class Solution {
public:
    int maxScore(vector<int>& cardPoints, int k) {
        int sum1 = 0, sum2 = 0;
        int p = 0, q = cardPoints.size() - 1
 
;
        int len = cardPoints.size();
        for(int i = 0; i < len && i < k; i++)
        {
            sum1 += cardPoints[i];
            sum2 += cardPoints[len - i - 1];
        }
        int ret = 0;
        int k1 = k, k2 = k;
        while(k)
        {
            if(sum1 >= sum2)
            {
                ret 
 
+= cardPoints[p];
                sum1 -= cardPoints[p];
                sum2 -= cardPoints[len - k2];
                k2--;
                p++;
            }
            else
            {
                ret += cardPoints[q];
                sum2 -= cardPoints[q];
                sum1 -= cardPoints[k1 - 1
 
];
                k1--;
                q--;
            }

            k--;
        }
        return ret;

    }
};