用于返回序列中最大可能的子序列总和的算法

int maxSumRec(const vector<int> &a, int left, int right){

    if (left == right){

               if (a[left] > 0){
        return a[left];
               }
               else
                  return 0;

    }

    int center = (left + right)/2;
    int maxLeftSum = maxSumRec(a, left, center);
    int maxRightSum = maxSumRec(a, center+1, right);

    int leftBorderSum = 0; int leftBorderMax = 0; 
    for (int i = center; i >= left; i--){

        leftBorderSum += a[i];
        if (leftBorderSum > leftBorderMax){

            leftBorderMax = leftBorderSum;
        }
    }

    int rightBorderSum = 0; int rightBorderMax = 0;
    for (int i = center+1; i <= right; i++){

        rightBorderSum += a[i];
        if (rightBorderSum > rightBorderMax){

            rightBorderMax = rightBorderSum;
        }

    }

    int crossSum = rightBorderMax + leftBorderMax;

    return max3(maxLeftSum, maxRightSum, crossSum);

}
int maxSumRec(const vector<int> &a, int left, i